The Effect of Light on Sleep and Sleep-Related Physiological Factors Among Patients in Healthcare Facilities: A Systematic Review

Abstract

Objectives:

Lighting is one of the environmental factors which can improve patient sleep in healthcare environments. Due to the high degree of variation in study designs and results on this topic, the implications have been difficult to interpret. This review consolidates studies on the impact of bright light exposure on sleep to identify lighting conditions that can be applied and researched in future healthcare environments.

Methods:

We searched for peer-reviewed articles on the impact of light on sleep or sleep-related outcomes in healthcare settings. We provided detailed analysis of the direct links between light and sleep, and a more cursory analysis of links between light and sleep-related factors, from 34 articles which met our inclusion criteria.

Results:

The current state of the literature includes evidence on how various durations and intensities of morning, midday, and evening bright light exposure, as well as whole-day light exposure interventions can improve specific aspects of sleep. Lighting interventions differed in all attributes (illuminance levels, exposure time, exposure duration, and spectral qualities) but showed promising results in improving patients’ sleep.

Conclusions:

Short-term bright light exposure in the morning, up to 2 hr of moderate (3,000–10,000 lux) morning exposures, up to 4 hr of moderate evening exposure, and whole-day exposures to lower illuminance levels (<3,000 lux) can improve patient sleep outcomes. Based on new findings on the mechanism through which light impacts sleep, future studies should be more specific about the spectral qualities of light sources.

Keywords

light phototherapy sleep circadian rhythm healthcare facilities;patient environment

Impaired sleep is associated with negative health outcomes (Joshi, 2008; Sloane et al., 2007). The consequences of poor sleep are particularly problematic for people with compromised health such as patients in hospitals and long-term care facilities. Many environmental factors, such as light, noise, air quality, and room temperature, as well as the layout of the room, can affect patient sleep (DuBose & Hadi, 2016). Light is the most powerful of the exogenous cues influencing the regulation of the endogenous pacemakers and entrainment of human circadian rhythms (Hood, Bruck, & Kennedy, 2004; Sloane et al., 2007). Recently discovered cells in the retina activate the circadian system in response to short-wavelength light distinct from the action of the visual system. The timing and duration of light exposure also significantly affect entrainment of the circadian rhythm (Hanford & Figueiro, 2013). We systematically reviewed the existing literature to understand how the use of light (from natural or artificial sources) can improve patient sleep in healthcare settings. The main focus of the article is on research that explores the impact of light on sleep, but we also discuss research on the effectiveness of light in regulating rest–activity, circadian rhythm, and hormonal changes.

Aims

The purpose of this study is to consolidate and evaluate the research studies on the effectiveness of lighting interventions on sleep and sleep-related physiological aspects (e.g., circadian or rest–activity rhythm) of patients in healthcare settings. A strong body of literature has highlighted secretion of hormones such as melatonin and serotonin as markers of circadian rhythmicity and sleep (Mishima et al., 1994; Mishima, Okawa, Shimizu, & Hishikawa, 2001; Okawa et al., 1991; Ursin, 2002). Therefore, the current review also sought studies that evaluated the effect of light interventions on these secondary outcomes of interest (circadian or rest–activity rhythm, melatonin, or serotonin) as indicators of potential impact on sleep. This literature review seeks to determine whether sufficient evidence exists to specify hospital lighting conditions to significantly improve patients’ sleep. It also aims to identify gaps in the literature in order to provide clear directions for the future light and sleep studies in healthcare.

Method

We searched Medline, CINAHL, PsycINFO, and the Web of Science for references in peer-reviewed journals published between January 1990 and April 2016 that pertained to light, illumination, or phototherapy targeting healthcare patient populations with the aim of improving sleep or related physiological factors (mechanisms or processes which affect human sleep). The search applied combinations of search terms relevant to outcomes of interest (Table 1). The following study designs were included throughout the search process: randomized controlled, quasi-randomized controlled, controlled before-and-after, historically controlled, cohort studies, and case-control studies. Since this study does not involve human subjects, institutional review board approval was not needed.

Table 1.

Search Strategy.

Database	Search Terms	#Hits
Medline	((MH “Outcome and Process Assessment (Health Care)+”) OR (MH “Sleep Disorders, Circadian Rhythm+”) OR (MH “Sleep Disorders+”) OR (MH “Adaptation, Psychological+”) OR (MH “Mood Disorders+”) OR (MH “Receptors, Melatonin+”) OR (MH “Serotonin+”) OR (MH “Vital Signs+”)) AND ((MH “Light+”) OR (MH “Phototherapy+”)) AND ((MH “Facility Design and Construction+”) OR (MH “Hospital Units+”) OR (MH “Hospitals+”) OR (MH “Residential Facilities+”))	89
CINAHL	((MH “Treatment Outcomes+”) OR (MH “Outcomes (Health Care)+”) OR (MH “Sleep Disorders+”) OR (MH “Sleep Disorders, Circadian Rhythm+”) OR (MH “Sleep Disorders, Intrinsic+”) OR (MH “Melatonin”) OR (MH “Serotonin”)) AND ((MH “Light+”) OR (MH “Phototherapy+”)) AND ((MH “Architecture+”) OR (MH “Environment and Public Health (Non-Cinahl)+”) OR (MH “Health Facilities+”) OR (MH “Home Health Care+”) OR (MH “Assisted Living”))	76
PsycINFO	(DE “Treatment Outcomes” OR DE “Psychotherapeutic Outcomes” OR DE “Sleep Disorders” OR DE “Hypersomnia” OR DE “Insomnia” OR DE “Kleine Levin Syndrome” OR DE “Narcolepsy” OR DE “Parasomnias” OR DE “Sleepwalking” OR DE “CLOCK Gene” OR DE “Sleep” OR DE “Napping” OR DE “NREM Sleep” OR DE “REM Sleep” OR DE “Biological Rhythms” OR DE “Animal Biological Rhythms” OR DE “Human Biological Rhythms” OR DE “Sleep Wake Cycle” OR DE “Consciousness States” OR DE “Awareness” OR DE “Flow (Consciousness State)” OR DE “Sleepiness” OR DE “Wakefulness” OR DE “Mental Disorders” OR DE “Adjustment Disorders” OR DE “Affective Disorders” DE “Hormones” OR DE “Melatonin” OR DE “Serotonin”) AND (DE “Visual Stimulation” OR DE “Illumination” OR DE “Visual Displays” OR DE “Visual Feedback” OR DE “Adaptation” OR DE “Environmental Adaptation” OR DE “Sensory Adaptation” OR DE “Sensory Adaptation” OR DE “Dark Adaptation” OR DE “Light Adaptation” OR DE “Phototherapy”) AND (DE “Environment” OR DE “Built Environment” OR DE “Facility Environment” OR DE “Therapeutic Environment” OR DE “Facility Environment” OR DE “Hospital Environment” OR DE “Architecture” OR DE “Interior Design” or DE “Furniture” OR DE “Facilities” OR DE “Community Facilities” OR DE “Correctional Institutions” OR DE “Residential Care Institutions” OR DE “Treatment Facilities” OR DE “Community Facilities” OR DE “Community Mental Health Centers” OR DE “Residential Care Institutions” OR DE “Hospitals” OR DE “Nursing Homes” OR DE “Clinics” OR DE “Health Care Services” OR DE “Continuum of Care” OR DE “Long Term Care” OR DE “Mental Health Services” OR DE “Palliative Care” OR DE “Primary Health Care” OR DE “Mental Health Services” OR DE “Community Mental Health Services” OR DE “Assisted Living”)	35
Web of Science	((sleep disorders) OR (circadian rhythm) OR (Sleep Wake Cycle)OR (Biological Rhythms) OR (mood disorders) OR(Consciousness) OR (Awareness) OR (Alertness) OR (melatonin) OR (serotonin) OR (Psychophysiology) OR (Insomnia) OR (Hypersomnia)) AND ((Light) OR (Illumination) OR (Phototherapy)) AND ((Built Environment) OR (Therapeutic Environment) OR (Hospital Environment) OR (Interior Design) OR (Furniture) OR (Facilities) OR (Hospitals) OR (Nursing Homes) OR (Long Term Care) OR (Assisted Living))	816
Total		1,016
After removing duplicates		988

Search Outcome

The search strategy produced 988 articles (Table 1) that were pared down to 78 after applying the inclusion and exclusion criteria to the titles and abstracts. The second screening of the 78 full texts led to the removal of 50 additional articles. Thus, 962 articles were excluded for lacking a focus on relevant study population, outcomes of interest, study designs, or not written in English. An additional eight articles identified from review articles were added to the final set (Figure 1) of 34; three articles in the final set report on the same study with minor changes in study population and outcomes (Fetveit & Bjorvatn, 2004, 2005; Fetveit, Skjerve, & Bjorvatn, 2003). From the final 34 articles, the following data were extracted and inserted into a table including setting, population, mean age, sample size, lighting intervention or exposure, intervention characteristics, outcome measure, and finding (Table 2).

Figure 1.

Flow chart of the study selection process.

Table 2.

Summary of Findings.

Reference	Setting	Population	Subjects	Age avg (SD)	Light Intervention	Light Source	Study Length	Light Exposure Duration	Illumination	Spectral Qualities	Outcomes on Sleep	Outcomes on Sleep-Related Variables	Findings on Sleep	Findings on Sleep-Related Outcomes
Martin, Marler, Harker, Josephson, and Alessi (2007)	Nursing home	Elderly patients	100	Intervention group: 87.8 (7.9), control group 86.3 (10.4)	Sunlight between 9:00 a.m. and 5:00 p.m.	Natural light	5 days	Minimum 30 min	≥20,000 lux	Not specified		Timing of mean activity level (mesor), α parameter of activity		The timing of mesor shifted significantly earlier in the intervention group from baseline to follow-up (06:49 to 06:03 a.m.) compared to the control group where it occurred later (06:12–06:49 a.m.; p = .22).The rest–activity rhythm α parameter (relative width of peak and trough) had a significant group by study phase difference with the control group deteriorating slightly compared to slight improvement in the activity level of the treatment group (p = .22)
Skjerve et al. (2004)	Psychogeriatric	Elderly patients with severe dementia and disturbed sleep patterns	10	79.4	Morning bright light between 8:00 a.m. and 10:00 a.m.	Desktop light therapy device	4 weeks	45 min	5,000–8,000 lux	Not specified	No improvement to sleep–wake disturbance measures	Time of peak activity (acrophase)		Acrophase time advanced significantly from 15:50 pretreatment to 14:48 during the fourth week of treatment (p = .05)
Sloane et al. (2007)	Geriatric units in psychiatric hospital and residential care facility	Elderly patients with dementia	66	79	Either bright light from 7:00 a.m. to 11:00 a.m., bright light from 4:00 p.m. to 8:00 p.m., bright light from 7:00 a.m. to 8:00 p.m., or standard lighting all day	Room level lighting system	3 weeks per lighting condition	A minimum of 1–2 hr	Approximately 2,500 lux, control condition approximately 600 lux	Not specified	Total sleep time, number of sleep bouts	Daytime sleepiness, acrophase, mesor, amplitude	Total night time sleep increased for all participants by 11 min (p = .04) and for residents with severe dementia by 16 min with morning bright light and 14 min with all day bright light compared with standard lighting (p < .001)	Morning bright light produced a mean phase advance of 29 min for the acrophase (p = .02)
Mishima, Hishikawa, and Okawa (1998)	Specialized ward	Patients with dementia	12 patients with vascular dementia (VD), 10 patients with dementia of Alzheimer’s type (DAT)	VD patients:81, DAT patients 78	Bright light or dim light from 9:00 a.m. to 11:00 a.m.	Fluorescent tubes around patient face	2 weeks	2 hr	Bright light (5,000–8,000 lux), dim light (300 lux)	Full-spectrum fluorescent		Nocturnal activity, percentage of the nocturnal activity to total activity		Light exposure significantly reduced nighttime activity counts per day (26.1 vs. 35.6) in the second week of treatment compared to the pretreatment period for VD patients, and compared with VD patients treated with dim light condition (26.1 vs. 32.5; p < .01). For the patients with DAT, bright light exposure did not improve rest–activity compared to pretreatment or to the dim light condition.Light exposure significantly reduced percentage of the nighttime activity to total activity (16.6% vs. 22.4%) compared to the pretreatment period and compared to dim light condition (16.6% vs. 21.1%) for VD patients (p < .01). For the patients with DAT, bright light exposure did not improve rest–activity compared to pretreatment or to the dim light condition
Ouslander et al. (2006)	Nursing home	Elderly residents	160	Group 1 83.5 (8.71), Group 2 82.9 (9.3)	Bright light from 5:00 p.m. to 8:00 p.m.	Light box	17 consecutive days and nights	Up to 2 hr	Approximately 1,467 lux	Full spectrum	Percentage of observations asleep during daytime		The mean values of percentage of observation of time asleep during the day significantly changed from baseline to intervention between the control and intervention group (p < .001). While this percentage decreased in intervention group by 7.8% (from 22.1 baseline to 13.8 intervention), it decreased only by 1.3% in the control group (from 19.6 baseline to 18.9)
Schnelle, Alessi, Al-Samarrai, Fricker, and Ouslander (1999)	Nursing home	Incontinent residents	230	Not specified	Minimizing number of light changes greater than 1-ft candle between 7:00 p.m. and 5:00 a.m.	Artificial light	Not specified	Not specified	A light change was recorded if there was approximately a 1-ft-candle (10.8 lux) change in light level	Not specified	Number of awakenings		There was a significant decrease in awakenings associated with light changes following the intervention (p < .001)
Akyar and Akdemir (2013)	Nursing home	Elderly with poor sleep quality	24	79.95 (3.49)	Morning bright light exposure	Light box, at the eye level at least 30 cm from the individual	1 month (4 weeks)	30 min each morning	10,000 lux	Cool white fluorescent, full spectrum	Sleep quality (mean scores of the global Pittsburgh Sleep Quality Index [PSQI])		The global quality scores were higher compared with preintervention and baseline scores (p < .001). The mean scores of the global sleep quality measure decreased from 12.87 at the beginning of the intervention to 3.95 after therapy and to 4.87 one month after therapy which shows the quality of sleep significantly improved with light therapy (higher scores indicate lower quality sleep)
Ancoli-Israel, Martin, Kripke, Marler, and Klauber (2002)	Nursing home	Residents with severe dementia and others with moderate to no dementia	77	85.7 (7.3)	Morning bright light from 9:30 a.m. to 11:30 a.m. Morning dim red light from 9:30 a.m. to 11:30 a.m. or evening bright light from 5:30 p.m. to 7:30 p.m.	Light box located one meter from the patient	18 days	2 hr	Bright light (2,500 lux), dim red light, (<300 lux)	Cool white fluorescent, full spectrum		Mean activity level (mesor), time of peak activity (acrophase)		Morning light treatment significantly delayed acrophase by 46 min (p = .022) and increased mesor by 0.116 (p = .027). Changes in evening light group were not significant
Chong, Tan, Tay, Wong, and Ancoli-Israel (2013)	Specialized delirium management unit in geriatric monitoring unit	Delirious patients	228	84.2 (7.4)	Evening bright light from 6:00 p.m. to 10:00 p.m.	Ceiling lights	Full length of stay	4 hr	2,000–3,000 lux	Not specified	Number of awakenings, total sleep duration	Length of first sleep bout, number of sleep bouts	Number of awakenings during the night decreased by 0.1 (p = .03) and total sleep time increased by 0.6 hr (p < .01) at discharge compared to baseline	Length of the first sleep bout increased by 0.6 hr (p < .01) and average number of sleep bouts decreased by 0.02 (p < .01) at discharge compared to baseline
Dowling et al. (2008)	Long-term care facilities	Residents with Alzheimer’s disease	50	86 (8)	Morning bright light from 9:30 a.m. to 10:30 a.m. with melatonin or placebo, compared to usual indoor light	Light box for treatment group and usual indoor light for the control group	10 weeks	1 hr a day for 5 days a week	>2,500 lux in gaze direction for intervention groups, 150–200 lux for control group	Not specified	Day: night sleep ratio, daytime sleep duration, nocturnal sleep duration	Circadian rhythm amplitude, circadian rhythmicity, daytime activity level, number and duration of sleep bouts, time of peak activity	No impact was found on nighttime sleep duration. Daytime sleep duration decreased by 66 min and day: night sleep ratio improved by 0.17 (p < .001) in the group treated with light and melatonin	Parametric amplitude was significantly better for the light plus melatonin group compared to light plus placebo and control groups (p = .002). Nonparametric measure of amplitude also significantly improved for this group compared to the light and placebo group (p = .002). Cosinor model goodness of fit (indicator of rest–activity rhythm) was significantly better in this group than in the control group (p = .008). The M10 (10 most active hours) significantly increased in this group compared to light and placebo (p = .003) and control groups (p = .007). Both treatment groups phase advanced and the control group phase delayed, but the differences were not significant. The differences in sleep bouts between groups were not significant
Fetveit and Bjorvatn (2004)	Nursing home	Patients with dementia	11	86.1 (8.9)	Bright light from 8:00 a.m. to 11:00 a.m.	Light box	2 weeks	2 hr	6,000–8,000 lux	Not specified	Sleep efficiency, sleep onset latency, total wake time, wake after sleep onset		Sleep efficiency remained significantly higher for more than 4 weeks posttreatment. Baseline sleep efficiency was 72.9%, which increased to 85.6% during treatment (p = .004). Sleep onset latency was significantly reduced from baseline of 1:17 hr to 0:17 during treatment (p = .01). Mean value of total wake time remained significantly reduced from 3:24 hr pretreatment to 1: 40 hr during treatment (p = .001). Mean value of wake after sleep onset did not change significantly (p = .233)
Fetveit and Bjorvatn (2005)	Nursing home	Patients with dementia	11	86.1 (8.9)	Bright light from 8:00 a.m. to 11:00 a.m.	Light box	2 weeks	2 hr	6,000–8,000 lux	Not specified	Average nap duration, total nap duration, daytime sleep		Bright light exposure was effective in reducing daytime sleep in nursing home patients with dementia. Average nap duration and total nap duration were both significantly reduced with bright light treatment (p = .004 and p = .046, respectively). Based on nursing staff diaries, daytime sleep was significantly reduced with treatment (p = .042)
Fetveit, Skjerve, and Bjorvatn (2003)	Nursing home	Patients with dementia	11	86.1 (8.9)	Bright light from 8:00 a.m. to 11:00 a.m.	Light box	2 weeks	2 hr	6,000–8,000 lux	Not specified	Early morning awakening, sleep efficiency, sleep onset latency, total wake time	Mesor, mean activity level, nocturnal activity	Mean value of early morning awakening (time from waking to rising) was significantly reduced from 0:16 pretreatment to 0:01 treatment (p = .027). Mean value of sleep efficiency significantly improved from 72.9% pretreatment to 85.6% during treatment (p = .006). Mean value of sleep onset latency was significantly reduced by 1 hr from 01:17 pretreatment to 00:17 during treatment (p = .011). Mean value of total wake time decreased significantly from 3:24 hr pretreatment to 1: 40 hr during treatment (p = .003)	Mean value of mesor significantly reduced from 58.3 pretreatment to 41.3 during treatment (p = .038). Mean value of night time activity significantly reduced from 45.1 pretreatment to 25.1 treatment (p = .037)
Figueiro et al. (2014)	Nursing home	Residents with Alzheimer’s disease and related dementia	14	86.9 (4.4)	Tailored lighting system which delivered moderate light levels and was turned on at the residents’ waking time (6:00 a.m. to 8:00 a.m.) and turned off at 6:00 p.m.	Fluorescent lamps	4 weeks	8–10 hr	66 lux baseline and 324 ± 190 lux intervention measured at the cornea	CCT of 9,325 K and spectral power distribution provided	Sleep quality (Global PSQI index), sleep efficiency, total sleep duration	Circadian phasor magnitude	The mean score of global PSQI index was significantly reduced during the intervention from 8.7 to 4.1 (p < .05). Mean value of sleep efficiency significantly improved from 80% baseline to 84% during the intervention (p = .03). Mean total sleep time during the intervention was significantly longer compared to the baseline (460 min vs.431 min; p = .03)	The mean phasor magnitude improved significantly from 0.27 at baseline to 0.35 during the intervention (p = .001)
Kobayashi et al. (2001)	Geriatric hospital	Inpatients	10	81.2 (8.8)	Bright light from 11:30 a.m. to 12:30 p.m.	Wall mounted fluorescent lamps	3 weeks	1 hr	8,000 lux for intervention, 1,000 lux before and after the intervention	Not specified	Daytime sleepiness		Drowsiness in the afternoon decreased significantly after light exposure (from 1.5 baseline to 1.3 after exposure on a 0–4 scale; p = .01)
Lyketsos, Veiel, Baker, and Steele (1999)	Chronic care facility	Patients with dementia	15	80.8 (8.7)	Morning bright light or dim light	Full-spectrum lamp	4 weeks	1 hr	10,000 lux for intervention group	Full-spectrum lamp for intervention and a dim, low frequency blinking light for control	Nocturnal sleep duration		Patients who received bright light therapy showed a significant increase in their nighttime sleep to 8.1 hr from the baseline of 6.4 hr (p < .05)
Mishima et al. (1994)	Geriatric ward at a psychiatric hospital	Patients with dementia and sleep disorder	14	75	Morning bright light therapy from 9:00 a.m. to 11:00 a.m.	Desktop light therapy device	4 weeks	2 hr	3,000–5,000 lux	Full spectrum	Daytime sleep duration, nocturnal sleep duration, total sleep duration		Nocturnal sleep time significantly increased in dementia patients to 6.7 hr after light therapy compared to 5.7 hr at baseline (p < .01). Total sleep time significantly increased in dementia patients to 7.6 hr after the light therapy compared to 7.1 hr at baseline (p < .05)
Mishima, Okawa, and Hishikawa (2001)	Nursing homes, community homes	Elderly residents with psychophysiological insomnia, healthy residents (EC), healthy young control subjects	30	Elderly residents with insomnia (74.2), healthy residents (72.7), healthy young control subjects (20.9)	Bright and midday light (morning from 10:00 a.m. to 12:00 p.m. and midday from 2:00 p.m. to 4:00 p.m.	Overhead fluorescent lamps	2-week baseline/4-week study period	4 hr	2,500 lux	Full spectrum	Number of awakenings	Melatonin amplitude, melatonin levels	Morning and midday light exposure (2 hr in the morning and 2 hr in the midday, a total of 4 hr each) significantly decreased mean number of awake times during the night in elderly residents with insomnia to 5.57 times compared to baseline value of 7.96 (p < .05)	Midday light exposure significantly increased mean value of melatonin rhythm amplitude in the elderly residents with insomnia from 18.5 pg/mL at baseline to 35.1 pg/mL after treatment (p < .05).Midday light exposure significantly increased the mean nocturnal melatonin secretion volume in the elderly residents with insomnia from 139.1 pg/mL.h baseline to 231.9 pg/mL.h posttreatment (p < .05)
Riemersma- van Der Lek et al. (2008)	Assisted care facility	Elderly residents	189	85.8 (5.5)	Whole-day bright (or dim light), crossed with daily intake of melatonin or placebo	Overhead fluorescent lamps	5 years	Whole day between approximately 9:00 a.m. and 6:00 p.m.	Bright light (±1,000 lux), dim light (±300 lux), measured before the eyes in the gaze direction	Not specified	Duration of awakenings, sleep efficiency, total sleep duration	Nocturnal restlessness, quantified as the minutes per hour containing any activity during the most restful 5-hr period	Combined bright light and melatonin treatment significantly reduced the average duration of individual brief nocturnal awakenings by 0.53 min per year to 0.21 from a baseline of 0.85 (p = .01). Combined bright light and melatonin treatment significantly increased sleep efficiency by 3.46%, moving from 73% at baseline for this group to 80% at 2 year mark (p = .01). Bright light treatment significantly increased sleep duration by 10 min per year over the 5 year period which equates to a 2% increase (p = .04)	Combined bright light and melatonin treatment significantly improved nocturnal restlessness by 1 min per hour each year over the course of study from 1.78 at baseline to 0.26 following treatment which equates to 9% (p = .01)
Ancoli-Israel et al. (2003)	Nursing home	Patients with Alzheimer’s Disease	92	82.3 (7.6)	Morning bright light from 9:30 a.m. to 11:30 a.m. morning dim red light from 9:30 a.m. to 11:30 a.m. or evening bright light from 5:30 p.m. to 7:30 p.m.	Light box located one meter from the patient	10 days	2 hr	Bright light (2,500 lux), dim red light, (<300 lux)	Cool white fluorescent, full spectrum	Total sleep time, wake after sleep onset, percent sleep, percent wake, number and duration of nighttime awakenings, duration and intervals between daytime naps	Sleep and wake bouts, circadian rhythmicity measured by the F statistic of the fit of the 5-parameter model	None of the three light treatment conditions had any significant effect on actigraphically measured sleep or wake during the day or night	Duration of the maximum sleep bout at night increased significantly in the morning light group (p = .05) and in the evening light group (p = .02). Changes in morning dim light group was not significant. Evening bright light improved circadian rhythmicity, measured by the increase of the F statistic of the fit of the 5-parameter model, for the rhythms based on the mean activity levels (p < .01) and for the rhythms based on the maximum activity level (p < .01). No significant effect was seen with the other groups
De Rui et al. (2015)	Inpatient hospital	Patients with cirrhosis of the liver	12	59 (15)	Dynamic light	Wall mounted lights	Full length of stay 8.4 (6.1) days	Controlled from 6:00 a.m. to 10:30 p.m.	500 lux in gaze direction	Blue-enriched 6,500 K in morning and red-enriched 3,000 K in afternoon/evening	Daytime sleepiness, sleep time, sleep quality (PSQI), Sleep Timing and Sleep Quality Sleep Questionnaire, sleep diaries	Melatonin metabolite 6- sulfatoxymelatonin (aMT6s)	No difference was found between treatment and control groups outcomes	No significant impact was observed on aMT6s
Dowling, Hubbard, Mastick, Luxenberg, Burr, and Van Someren (2005)	Long-term care facilities	Residents with Alzheimer’s disease	46	84 (10)	Morning bright light from 9:30 a.m. to 10:30 a.m.	Light box for treatment group and usual indoor light for the control group	10 weeks	1 hr a day for 5 days a week	>2,500 lux in gaze direction (mean = 7,500 lux, SD = 9,500), 150–200 lux for control group	Not specified	Daytime wake time, nighttime sleep efficiency, nighttime wake time, nocturnal sleep duration, number of awakenings	Rest–activity rhythm, amplitude, acrophase, inter-daily stability, intra-daily variability, L5, M10, relative amplitude	No significant difference between intervention and control groups for all sleep variables	No significant difference was observed in circadian variables between intervention and control groups
Dowling, Mastick, Hubbard, Luxenberg, and Burr (2005)	Long-term care facilities	Residents with Alzheimer’s disease	70	84 (10)	Morning bright light from 9:30 a.m. to 10:30 a.m. or evening bright light from 3:30 p.m. to 4:30 p.m.	Light box for treatment group and usual indoor light for the control group	10 weeks	1 hr a day for 5 days a week	>2,500 lux in gaze direction, 150–200 lux for control group	Not specified	Sleep efficiency, sleep time, wake time, number of awakenings, duration of awakenings	Rest activity–rhythm, amplitude, acrophase	No significant difference between intervention and control group for all sleep variables	No significant difference was observed in rest–activity rhythms or amplitudes of intervention and control groups. The timing of the acrophase remained relatively stable in both experimental groups in significant contrast to the control group that had a 131 min delay in acrophase over the 10 week period (p < .04)
Figueiro (2008)	Senior healthcare facility	Alzheimer’s disease and non-Alzheimer’s disease patients	6	Not specified	Blue or red light from 4:30 p.m. to 6:30 p.m.	LEDs tabletop luminaires, ceiling luminaires with fluorescent lamps	2 weeks	2 hr	30 lux at cornea from LED tabletop luminaires, 300 lux on the table by ceiling luminaires containing fluorescent lamps	Blue (lambda max = 470 nm) for intervention, red light (lambda max = 640 nm) for control, ceiling luminaires CCT of 4,100 K	Percentage of observations asleep during night		Non-AD subjects were found asleep 89.5% of the time at night following blue light exposure and 67% of the time on evenings following red light exposure. This effect was not significant for patients with Alzheimer’s. Nighttime sleep efficiency was significantly higher after blue light than after red light (p = .0003)
Gasio, Kräuchi, Cajochen, Someren, Someren, Eus van Amrhein, Pache, Savaskan, and Wirz-Justice (2003)	Nursing home	Patients with dementia	13	85 (5)	Dawn–dusk simulator: gradually changing light levels or constant dim red light at both dawn and dusk	Overhead halogen lamps	3 weeks	Whole day	Intervention (0.001–210 lux), control (<5 lux)	White light for intervention, red light for control	Total sleep time, sleep efficiency, sleep latency, time in bed, sleep start and end, number of awakenings, number of immobile phases, activity during sleep	Inter-daily variability of activity, circadian rhythm amplitude, intra-daily stability of activity	No difference was found between treatment and control group for all sleep variables	No difference was found between treatment and control group for all sleep-related variables
Koyama et al. (1999)	Nursing homes	Patients with dementia	6	86.1	Bright light from 9:30 a.m. to 11:30 a.m. or from 11:00 a.m. to 12:00 p.m.	Desktop type and flat panel tray type	30–96 days	1–2 hr	4,000 lux at eye level	Not specified	Percentage of observations asleep during lights-out period (sleep efficiency), percentage of observations asleep during daytime, sleep onset time		During the bright light period sleep efficiency significantly increased in three subjects. During the bright light period, percentage of time observed awake in daytime significantly increased in three subjects. During the bright light period, sleep onset timing became significantly earlier in 3 subjects
LaReau, Benson, Watcharotone, and Manguba (2008)	Cardiology and adult medical units	Elderly patients	59	79.6 (7.78)	Sleep protocol intervention darkening light levels in rooms to patient preference. Control group received usual care	Not specified	5 days	Whole day	Not specified	Not specified	Number of awakenings, sleep quality defined by Richards–Campbell Sleep Questionnaire, total sleep duration		No significant difference was observed between the intervention and control group
Lee, Aycock, and Moloney (2013)	Neonatal intensive care unit	Mothers of low-birth-weight infants	30	26.6 (6.3)	Bright light therapy intervention with blue-green light visor versus control group wearing a red-light visor during the first waking hour	Light visor fixed close to eyes	3 weeks	30 min	8,000 lux intervention group, 5 lux control group	Blue-green light 470–525 nm) for intervention, red light for control	Self-reported sleep quality (General Sleep Disturbance Scale), total sleep duration	Circadian activity measures (amplitude, mesor)	No significant difference between the intervention and control groups was found for all sleep variables	No significant difference between the groups was found
Royer et al. (2012)	Long-term care facilities	Elderly residents	28	Treatment group 84.3, placebo group 86.4	Blue or red light starting at 9:30 a.m. or 10:30 a.m.	Color LED luminaires, composed of red-green-blue light-emitting diodes	Monday through Friday for 4 weeks	30 min	400 lux of blue light), approximately 75 lux of red light	Blue light peak of 464 nm, red right peak of 628 nm. The circadian stimulus values were 1.714 for blue and 0.014 for red	Daytime sleepiness		No significant changes were detected in reports of daytime sleepiness
Taguchi, Yano, and Kido (2007)	Postoperative ICU	Postsurgical esophageal cancer patients	11 (6 in treatment group, 5 in control group)	57.6	Bright light from 7:30 a.m. to 9:30 a.m.	Fluorescent lamps mounted in a stand	2.8 (0.9) starting day after extubation until discharge	2 hr	5,000 lux	Three wavelengths, otherwise unspecified		Nocturnal activity		No significant difference was noted in the activity level between the two groups
Van Someren, Kessler, Mirmiran, and Swaab (1997)	Psychogeriatric ward	Patients with Alzheimer’s disease or dementia	22	79 (2)	Whole-day bright light in living room	Overhead	4 weeks	Whole day	Intervention (average 1,136 lux), baseline (average 436 lux)	Not specified		Inter-daily stability of activity, intra-daily variability of activity		The stability of the rest–activity rhythm (IS) during the light treatment intervention was significantly higher compared to the baseline for patients with intact vision (p < .002). The fragmentation of rest–activity rhythm (IV) was significantly lower during the lighting intervention compared to the baseline for patients with intact vision (p < .01)
Wu, Sung, Lee, and Smith (2015)	Long-term care facility	Elderly residents	65 (34 experimental, 31 control)	Experimental group 80.97 (9.84) control group 79.03 (10.06)	Bright light from 9:30 a.m. to 10:00 a.m.	Light box	3 times a week for a 4-week period	30 min	10,000 lux	Not specified	Sleep disturbances		No significant difference between mean scores of sleep disruptions was found between the intervention and the control group
Simons, Laheij, van den Boogaard, Moviat, Paling, Polderman, Rozendaal, Salet, van der Hoeven & Pickkers (2016)	ICU	Patients over 18 with expected length of stay > 24 hr	734 for delirium, 20 for melatonin metabolites	Intervention group:66.3 (12.8), control group 64.4 (13.7)	Dynamic lighting	Overhead fluorescent lamps	Full length of stay	Whole day	Intervention (1,700 lux from 9:30 a.m. to 11:30 a.m. and 1:30 p.m. to 4:00 p.m.), control group (300 lux)	Intervention at 4,500 K from 9:30 a.m. to 11:30 a.m. and 1:30 p.m. to 4:00 p.m. with 3,000 K during rest period, 3,000 K all day for control		6-sulfatoxymelatonin excretion, cortisol level		Daytime bright light exposure made no significance difference in 6-sulphatoxymelatonin or cortisol excretion
Satlin, Volicer, Ross, Herz, and Campbell (1992)	Inpatient hospital	Patients with Alzheimer’s disease	10	70.1 (5.1)	Bright light (evening) from 7:00 p.m. to 9:00 p.m.	Light box	1 week	2 hr	1,500–2,000 lux	Not specified	Clinical ratings of sleep–wakefulness disturbances	Circadian rhythm amplitude, intra-daily variability of activity, percentage of the nocturnal activity to total activity, time of peak activity	The mean score of sleep–wakefulness disturbances of all patients decreased from 6.2 a night at baseline to 3.0 during treatment and 2.3 posttreatment (p = .03)	The mean relative amplitude significantly increased from 0.65 at baseline to 0.9 during treatment week (p = .02). The mean score of intra-daily variability decreased significantly from 1.04 at baseline to 0.71 during the treatment (p = .03). The mean percent of nocturnal activity significantly declined from 18.4% at baseline to 11.6% during treatment (p = .02)

Results

Organization of Heterogeneous Findings

Studies included in our review investigated the impact of light on a variety of patient sleep measures including sleep quality, total sleep time (TST), nocturnal sleep time, diurnal sleep time, nocturnal wake time, awakenings, daytime wake time, sleep efficiency, sleep onset time, sleep disturbances, and daytime sleepiness. In a less detailed manner, we also reviewed and reported studies that investigated the impact of light on sleep-related factors including rest–activity measures, circadian rhythmicity, and sleep hormones such as melatonin and serotonin.

The timing of lighting interventions applied in these studies fall into several categories such as morning, midday, evening, whole day, and tailored dynamic lighting systems. They also vary immensely in duration of exposure, length of the lighting intervention study, illuminance, and spectral qualities. The mechanism for delivering the lighting interventions includes natural light exposure, light box, florescent lamps, LED luminaires, and light visors. Additionally, there is great variability in the level of detail provided on spectral quality and light source. To deal with the heterogeneity of these studies, we organized the findings by sleep outcomes and within this category further grouped the studies by type of lighting intervention. A summary of findings and details of the interventions is presented in Table 2.

Lighting is a great nonpharmacological option for improving sleep in healthcare populations, so we were interested to determining the potential impact even if we could not be definitive about the specific conditions and effects. That being the case, we used the following language conventions when summarizing the findings. When there are multiple studies with some having significant findings and others not finding a significant impact, we use the term “can” to express that there is some evidence that light has that impact. If none of the studies have significant findings, either positive or negative, we describe the relationship as “may” impact the outcome. In the few cases where all the research agrees, we state the impact directly.

Impact of Light on Sleep

Impact of light on sleep quality

Sleep quality is usually measured through self-reported questionnaires such as Pittsburgh Sleep Quality Index (PSQI), Richards–Campbell Sleep Questionnaire, General Sleep Disturbance Scale (GSDS), and Sleep Timing and Sleep Quality Sleep Questionnaire. Although all of these measurement methods evaluate the quality of sleep on a numerical measure, with higher scores indicating worse sleep, the questions and scales of the studies vary. The current review identified that 30 min of full-spectrum morning bright light (10,000 lux) exposure, and tailored lighting systems (66–324 lux, white 9,325 K CCT) can improve the quality of patient sleep measured by self-reported questionnaires.

Morning bright light exposure can improve sleep quality

Various types of morning bright light therapies can improve the quality of patients’ sleep. Twenty-four older adults in a nursing home were exposed to 30 min of 10,000 lux full-spectrum light every morning for a month. The mean PSQI global sleep quality measure decreased from 12.87 (out of a maximum of 21) at the beginning of the intervention to 3.95 after therapy and was still markedly lower than baseline (4.87) at the 1-month follow-up (p < .001; Akyar & Akdemir, 2013). Another study with 30 min of 8,000 lux blue-green light (wavelengths 470–525 nm) reported improved sleep quality measured by GSDS, but this was not significant (Lee, Aycock, & Moloney, 2013).

Tailored dynamic whole-day light systems (06:00–18:00) can improve sleep quality

A study of 14 patients with Alzheimer’s disease (AD) and related dementia showed significant improvement in sleep quality using a tailored lighting system delivering moderate light levels from a high correlated color-temperature white light source (9,325 K) for 4 weeks. The lighting system was turned on at the residents’ waking time (between 06:00 and 08:00) and switched off at 18:00. The mean light level at baseline was 66 lux at the cornea, compared to 324 lux during the intervention. The mean global PSQI score was significantly reduced during the intervention compared to baseline (8.7–4.1, p = .01; Figueiro et al., 2014). Another study did not find significant improvement on any of the sleep quality measures (De Rui et al., 2015).

Impact of light on TST

TST is the cumulative time in sleep episodes occurring day or night (total sleep episodes less the wake time). A 2 hr of full-spectrum 3,000–5,000 lux of morning light exposure, constant whole-day (06:00–17:00) bright light exposure of 1,000 lux, and a tailored dynamic whole-day (06:00–22:00) lighting system (324 lux mean light level and CCT of 9,325 K) can increase TST by 30, 10, and 29 min, respectively.

Morning bright light therapy can increase TST

The effect of morning bright light exposure (3,000–5,000 lux, 09:00–11:00, for 4 weeks) on the sleep of 14 elderly patients with dementia and sleep disorders at a psychiatric hospital was compared to 10 control elderly patients from the general ward of the same hospital. TST of the elderly patients with dementia was significantly shorter than that of the control group (7.1 vs. 8.2 hr) at baseline and increased significantly to 7.6 hr during the intervention (Mishima et al., 1994). Other studies of morning bright light therapy with shorter durations of light exposure did not find significant improvements in TST (Dowling et al., 2008; Lee et al., 2013).

Evening bright light therapy, as a part of multicomponent intervention, may increase TST

In the only study on evening light exposure, bright light therapy (2,000–3,000 lux) was delivered through ceiling lights from 18:00 to 22:00 as part of a multicomponent sleep hygiene program to improve sleep in delirious older adults of a geriatric monitoring unit (GMU). Data from nurse-collected logs showed significant improvements in TST at discharge compared to baseline (7.7 vs. 7.1 hr, p < .01; Chong, Tan, Tay, Wong, & Ancoli-Israel, 2013); it is not clear whether the effect was from evening bright light therapy or results of other interventions in the sleep hygiene program. A multicomponent study including darkening light levels at nights did not observe significant improvements in TST (LaReau, Benson, Watcharotone, & Manguba, 2008).

Tailored dynamic whole-day light systems (06:00–18:00) can increase TST

Mean TST was significantly longer compared to baseline (460 vs. 431 min, p = .03) after 4 weeks of a tailored lighting system (324 lux mean light level and CCT of 9325 K), from first thing in the morning (06:00–08:00 to 18:00; Figueiro et al., 2014). A shorter study of a full-day dynamic lighting system (maximum 500 lux in gaze direction from 06:00 to 20:30) did not show significant improvements in TST for severely ill cirrhosis patients (De Rui et al., 2015).

Whole-day bright light (1,000 lux from 06:00 to 21:00) increases TST

In a controlled trial, dementia patients in 12 assisted care facilities were randomly assigned to one of two light conditions (whole-day exposure to an average 1,000 lux bright light or to an average 300 lux dim light between 09:00 and 18:00), and participants were assigned a daily intake of either melatonin or placebo for 15 months. Bright light significantly increased sleep duration by 10 min (2%) per year (p = .04; Riemersma-van Der Lek et al., 2008). Melatonin-only treatment also significantly increased TST (27 min or 6%, p = .004), but the combined treatment (light and melatonin) did not show significant improvements.

Impact of light on nocturnal sleep time

Another sleep variable of interest is the duration of sleep during the night. A 2 hr of full-spectrum 3,000–5,000 lux and 1 hr of 10,000 lux morning bright light exposure can increase nocturnal sleep time by 1 and 1.7 hr, respectively.

Morning bright light therapy can improve nighttime sleep time

A before-and-after study on the effect of 2-hr full-spectrum morning bright light exposure (3,000–5,000 lux, 09:00–11:00, for 4 weeks) on the sleep of elderly patients with dementia showed a significant increase in mean nocturnal sleep time after light therapy compared to baseline (6.7 vs. 5.7 hr; Mishima et al., 1994). Another randomized controlled trial on demented patients in a chronic care facility found that 1-hr morning exposure of 10,000 lux light for 4 weeks significantly increased nocturnal sleep time (6.4–8.1 hr) compared to the dim light control group (illuminance levels unspecified; Lyketsos, Veiel, Baker, & Steele, 1999). However, other studies did not find any significant increase in nocturnal sleep time from morning light exposure (Dowling, Hubbard et al., 2005; Dowling, Mastick, Hubbard, Luxenberg, & Burr, 2005).

Impact of light on diurnal sleep time

Daytime sleep has a different structure than nighttime sleep and is not as restorative (Evans & French, 1995). A 2-hr light exposure of 3,000–5,000 lux and 1-hr morning exposure of >2,500 lux, in conjunction with an evening dose of melatonin, have significantly decreased the diurnal sleep duration by 18 and 66 min, respectively.

Morning bright light therapy can reduce diurnal sleep time

In the aforementioned Mishima et al. (1994) study, 2-hr bright light exposure of 3,000–5,000 lux for 4 weeks showed a significant decrease in daytime sleep of demented patients compared to baseline (1 vs. 1.3 hr; Mishima et al., 1994). Another randomized controlled trial showed that 1-hr daily morning bright light exposure (09:30–10:30, >2,500 lux in gaze direction for 10 weeks) plus an evening dose of melatonin, significantly decreased patients’ daytime sleep (249 min vs. 315 baseline) compared to the control group (150–200 lux), significantly improving the ratio of day/night sleep from 0.7 at baseline to 0.53 posttreatment (Dowling et al., 2008). However, the lighting intervention was combined with evening intake of melatonin, so it is not possible to attribute the result entirely to the lighting intervention.

Evening bright light therapy may reduce diurnal sleep time

Elderly residents of eight community homes completed a quasi-randomized controlled trial, which included evening bright light exposure (17:00–20:00) for up to 2 hr of approximately 1,467 lux full-spectrum bright light, in addition to other sleep hygiene strategies. After the intervention was implemented, residents were less frequently observed sleeping during the day (from 22.1% of observations at baseline to 13.8% during the intervention; p < .001; Ouslander et al., 2006). As a multicomponent intervention, it is not certain that the decrease in diurnal sleep was due to the evening bright light therapy.

Impact of light on nocturnal awakenings

About 2 hr of morning bright light exposure of 6,000–8,000 lux can reduce total nocturnal wake time, early morning awakenings, and wake after sleep onset time. Nearly 4 hr of midday bright light exposure of 2,500 lux can reduce awake times. About 4 hr of evening bright light exposure of 2,000–3,000 lux, as a part of a multicomponent program, may also reduce the number of awakenings. Whole-day exposure to an average 1,000 lux bright light combined with melatonin treatment may decrease the duration of awakenings.

Morning bright light exposure can reduce the duration of early morning and nighttime awakenings

About 2 hr of morning bright light exposure (6,000–8,000 lux, between 08:00 and 11:00, for 2 weeks) was significantly associated with reduced early morning awakening time (0:16 pretreatment to 0:01 during treatment), reduced total nocturnal wake time (3:24 hr pretreatment to 1:40 hr during treatment), and wake after sleep onset time (1:49 pretreatment to 1:23 treatment) of demented patients in nursing homes (Fetveit & Bjorvatn, 2004, 2005; Fetveit et al., 2003). Other studies on morning bright light exposures with shorter duration did not show significant changes in number of nighttime awakenings (Dowling, Hubbard et al., 2005; Dowling, Mastick et al., 2005).

Midday light exposure can reduce the number of nocturnal awakenings

In a cohort study, 4 hr of midday bright light exposure (2,500 lux; from 10:00 to 12:00 and 14:00 to 16:00 for 4 weeks) significantly decreased mean nocturnal awake times in the elderly residents with insomnia compared to baseline (5.57 vs. 7.96 times) measured by actigraphy (Mishima et al., 2001). Other studies with afternoon light exposure did not show significant changes in nighttime wake times (Dowling et al., 2005).

Evening bright light exposure may reduce the number of nocturnal awakenings

Nearly 4 hr of evening bright light exposure (2,000–3,000 lux; from 18:00 to 22:00), as a part of a multicomponent program during the full length of patient stay, was significantly associated with fewer number of observed nocturnal awakenings (0.6 vs. 0.7; p < .05) in 228 delirious older adults (Chong et al., 2013).

Limiting light exposure during nighttime can reduce awakenings

In a study of nursing home residents, the number of changes in light levels (greater than 10 lux change) at night was significantly associated with awakenings (Schnelle, Alessi, Al-Samarrai, Fricker, & Ouslander, 1999). Other multicomponent sleep protocols with light interventions did not show significant changes in awakenings (LaReau et al., 2008).

Whole-day light exposure (morning to evening) may reduce the duration of nocturnal awakenings

In the Riemersma-van Der Lek et al. (2008) study mentioned earlier, whole-day exposure to an average 1,000 lux bright light from 09:00 to 18:00 for the full length of stay, combined with melatonin treatment, reduced the average duration of individual brief nocturnal awakenings by 0.53 min per year or a relative 12% (0.85–0.21; p = .01; Riemersma-van Der Lek et al., 2008).

Impact of light on daytime wake times

Morning bright light exposure can increase daytime wake time

Morning bright light exposure (4,000 lux; 1–2 hr; between 09:30 and 11:30; for the full length of stay) was applied to six elderly demented residents of two nursing homes. Wake in daytime increased significantly in three subjects; however, due to the small sample size of the study and inconsistent results, the findings may not be generalizable (Koyama, Matsubara, & Nakano, 1999). Another study on the impact of morning light exposure on daytime wake times did not find any significant results (Dowling, Hubbard et al., 2005).

Impact of light on sleep efficiency

Sleep efficiency is the ratio of total nocturnal sleep time to the total amount of time spent in bed. About 2 hr of morning bright light exposure (6,000–8,000 lux), a tailored lighting system with bluish-white light (324 lux; morning to evening), and long-term whole-day bright light treatment (1,000 lux, morning to evening), when combined with melatonin intake, can improve sleep efficiency by 12.7, 4, and 3.46%.

Morning bright light exposure improves sleep efficiency

Morning bright light exposure has been shown to be very effective in improving sleep efficiency. About 2 hr of morning bright light exposure (6,000–8,000 lux between 08:00 and 11:00 for 2 weeks) improved the sleep efficiency of demented patients in nursing homes. Sleep efficiency remained significantly higher for more than 4 weeks posttreatment (85.6% immediately following treatment vs. 72.9% baseline, p = .006; 77.5% 4 weeks after treatment vs. 72.9% baseline, p = .049; Fetveit & Bjorvatn, 2004, 2005; Fetveit et al., 2003). In the Koyama, Matsubara, and Nakano (1999) study of the effects of morning bright light exposure (1–2 hr of 4,000 lux light) on six demented patients, the percentage of sleep during lights-out (sleep efficiency) significantly increased in half of the already small sample minimizing the significance of the results (Koyama et al., 1999).

Evening light exposure may improve sleep efficiency

A sample of three AD residents and three non-AD residents with sleep complaints were exposed to 30 lux of blue or red light at the cornea for 2 weeks between 16:30 and 18:30. Non-AD subjects were found asleep during the night more often after exposure to blue light versus red light (89.5% of the time vs. 67% of the time). A similar but insignificant trend was observed with the AD patients (Figueiro, 2008). This study suggested the effectiveness of narrowband blue light in improving sleep, but the study sample was very small.

Tailored whole-day light systems (morning to evening) improves total sleep efficiency

In the Figueiro et al. (2014) study, a tailored lighting system delivering moderate levels of bluish-white light (324 lux; between 06:00–08:00 and 18:00) was associated with better sleep efficiency scores during intervention versus baseline (84% vs. 80%, p = .03). Long-term (average of 15 months) whole-day bright light treatment (1,000 lux, 09:00–18:00), combined with melatonin intake, significantly increased sleep efficiency of elderly residents of an assisted care facility by 3.46% (p = .01) compared to the dim light control (300 lux; Riemersma-van Der Lek et al., 2008).

Impact of light on sleep onset latency

Sleep onset latency is the time that it takes to transition from full wakefulness to sleep; bright morning light has been shown to improve latency.

Morning bright light exposure improves sleep latency

Morning bright light exposure can shift sleep onset time earlier and reduce sleep onset latency. In Fetveit’s study of 11 demented nursing home patients, 2 hr of morning bright light exposure (6,000–8,000 lux between 08:00 and 11:00 for 2 weeks) was associated with a significant reduction in sleep onset latency (01:17 pretreatment to 00:17 treatment; Fetveit & Bjorvatn, 2005; Fetveit et al., 2003). Another study found that sleep onset latency remained significantly reduced 12 weeks posttreatment (Fetveit & Bjorvatn, 2004). In the Koyama et al. study of morning bright light exposure (1–2 hr of 4,000 lux light) with six demented patients, sleep onset advanced to earlier in the evening in three of six subjects (Koyama et al., 1999).

Impact of light on sleep disturbances

The current review identified that 2 hr of evening light exposure of 1,500–2,000 lux may reduce clinical rating of sleep disturbances.

Morning bright light exposure does not reduce sleep disturbances

A recent study examining the impact of morning bright light therapy (30 min of 10,000 lux, 09:30–10:00, 3 times per week for 4 weeks) on sleep disruptions of 32 elderly long-term care residents found no significant difference between mean scores of sleep disruptions between the intervention and control group (Wu, Sung, Lee, & Smith, 2015).

Evening bright light exposure reduces sleep disturbances

Evening bright light therapy has been shown to improve the rest–activity rhythm of inpatients with Alzheimer’s and disturbed sleep. In this before-and-after study, 10 patients were exposed to 2 hr of evening (19:00–21:00) bright light (1,500–2,000 lux) for a week. The mean score of sleep–wakefulness disturbances of all patients, as rated by nurses, decreased from 6.2 at baseline to 3.0 during the treatment and 2.3 posttreatment (p < .05; Satlin, Volicer, Ross, Herz, & Campbell, 1992).

Impact of light on daytime sleepiness

Morning bright light exposure can reduce daytime sleepiness

Ten elderly patients with sleep disturbances were studied before-and-after exposure to approximately 8,000 lux bright light for 1 hr during their lunch time (11:30–12:30) over 3 weeks. About 3 weeks before and after the intervention, subjects had their lunch under approximately 1,000 lux light. During the intervention, nurse-rated afternoon drowsiness decreased significantly (from 1.5 baseline to 1.3 after exposure on a 0–4 scale; p = .01; Kobayashi et al., 2001). Other lighting solutions did not improve self-reported daytime sleepiness measures (De Rui et al., 2015; Royer et al., 2012).

Impact of Light on Sleep-Related Physiological Markers

We summarize here the lighting interventions that demonstrate significant impacts on sleep-related physiological factors such as rest–activity measures, circadian rhythmicity, and sleep hormones in association with light (see Table 2 for details). The rest–activity rhythm and circadian measures explained here are nighttime activity level, mean activity level during the 10 most active hours (M10), mean activity level (mesor), resonance between light–dark and rest–activity patterns across 24 hr (phasor magnitude), time of the peak activity (acrophase), difference between activity peaks and troughs (amplitude), number and duration of sleep bouts, fragmentation of rest–activity rhythm (intra-daily variability [IV]), stability of the rest–activity rhythm (inter-daily stability [IS]), the rest–activity rhythm α parameter (relative width of peak and trough), and rhythmicity of the circadian rhythm. Hormonal changes related to sleep are also reported.

Morning light exposure

About 2 hr of morning bright light therapy of 6,000–8,000 lux significantly reduced the mean value of nighttime activity and mean value of mesor in dementia patients (Fetveit & Bjorvatn, 2005; Fetveit et al., 2003). Another 2-hr morning bright light intervention on dementia patients using 5,000–8,000 lux also showed significant reduction in nighttime activity counts per day, as well as a reduction of the ratio of nighttime activity to total activity for patients with vascular dementia (Mishima, Hishikawa, & Okawa, 1998). Morning light exposure of shorter duration (1 hr of >2,500 lux), combined with melatonin intake, also significantly increased M10 in Alzheimer’s patients and the amplitude of the rest–activity rhythm. In addition, nonparametric measure of amplitude significantly improved for the light and melatonin. Rest–activity rhythm, indicated by an improvement in the goodness of fit (R2) of the data to a traditional cosinor model, also improved significantly (Dowling et al., 2008). Another study with 2-hr bright light exposure on demented patients (2,500 lux) showed that increased exposure to morning bright light was significantly associated with an increased mean activity level and a delayed acrophase (Ancoli-Israel, Martin, Kripke, Marler, & Klauber, 2002). On the contrary, acrophase was significantly advanced by 45 min of morning bright exposure of 5,000–8,000 lux in demented patients (Skjerve et al., 2004). It was also significantly advanced by morning bright light exposure (1–2 hr of 2,500 lux) in another group of demented patients (Sloane et al., 2007).

Evening light exposure

Evening exposure to bright light (2,500 lux) for 1–2 hr produced a significant delay in acrophase for patients with dementia (Sloane et al., 2007). It also significantly increased amplitude of the rhythm, decreased the mean score of IV, and decreased the mean percent of nocturnal activity in Alzheimer’s patients where they were exposed to 1,500–2,000 lux for 2 hr (Satlin et al., 1992). In another study on Alzheimer’s patients, 2 hr of 2,500 lux evening light exposure improved circadian rhythmicity (Ancoli-Israel et al., 2003). Longer duration of evening light exposure (4 hr of 2,000–3,000 lux) significantly increased length of the first sleep bout and number of sleep bouts at discharge in patients with delirium (Chong et al., 2013).

Midday light exposure

Exposure to 4 hr of bright light (2,500 lux) in two sessions (morning and afternoon) significantly increased mean value of melatonin parameters AMP (the difference between peak and low values) and ACUn (in elderly residents with insomnia (Mishima et al., 2001).

Whole-day light exposure

Long-term daily treatment with morning to evening bright light (1,000 lux), combined with melatonin intake, significantly improved nocturnal restlessness in elderly residents (Riemersma-van Der Lek et al., 2008). Another multicomponent intervention exposed participants to >20,000 lux of direct sunlight for at least 30 min between the hours of 09:00 and 17:00, shifted the timing of the mesor significantly earlier and changed the α parameter of the rest–activity rhythm in elderly residents (Martin, Marler, Harker, Josephson, & Alessi, 2007). Exposure to a tailored lighting system which delivered moderate light levels (324 lux) and was illuminated between waking time and evening changed the phasor magnitude significantly in Alzheimer’s patients (Figueiro et al., 2014). Another study with whole-day bright light exposure (1,136 lux) on Alzheimer’s patients also showed significantly lowered IV and increased IS (Van Someren, Kessler, Mirmiran, & Swaab, 1997).

Various Light Exposure Conditions Associated With Significant Sleep Outcomes

Out of 34 studies reviewed for this article, 14 studies investigated the impact of light on sleep outcomes, 10 studies on sleep-related outcomes, and 10 studies on both sleep and sleep-related outcomes. Among 24 studies on sleep outcomes, 16 studies were associated with statistically significant results. For 20 studies on sleep-related outcomes, 13 studies showed statistically significant results. Figure 2 illustrates an overview of illuminance (lux) and the time/duration of exposure of the lighting interventions of 15 studies that showed significant results in sleep outcomes; one study was excluded (Schnelle et al., 1999) because it did not specify illuminance and timing/duration of light. Figure 4 illustrates the lighting interventions of the 16 studies that showed significant results in sleep and sleep-related outcomes. In studies comparing outcomes between lighting intervention and control groups, we considered the impact of lighting intervention significant if the outcomes were significantly different between the intervention and control groups.

Figure 2.

Light interventions with significant sleep improvements. In this figure, the lighting interventions are shown with two parameters: illuminance and time of the exposure. The width of each rectangle shows the time of the day when subjects were exposed to light and the height shows the illuminance levels. If the timing of light exposure was not reported clearly (ex, 2 hours of 6,000-8,00 lux between 08:00 and 11:00 for study 4,5,6), the dashed rectangle shows the bounds of exposure time. If the illuminance level was reported as more then specific lux values (ex, more that 250 for study 3), then it is shown in the diagram as a pointed rectangle.

Figure 3.

Associations between certain characteristics of light interventions and significant sleep improvements.

Figure 4.

Light interventions with significant sleep-related outcome improvements.

Studies using higher illuminance levels had an impact despite shorter light exposure durations in comparison with the studies using lower illuminance levels. Light conditions (1, 10 in Figure 2) with high illuminance levels (≥10,000 lux) were effective even with short-term exposure (30–60 min); light conditions (4, 5, 6, 9, 11) with moderate illuminance levels (3,000–10,000 lux) were effective with relatively longer exposure (1–2 hr). Lighting conditions (2, 3, 7, 8, 12, 13, 14, 16) with lower illuminance levels (≤3,000 lux) tended to have even longer exposure (1–4 hr or whole day). For those with significant results in sleep measures, as shown in Figure 2, the timing of light exposure also varied. Our analysis shows that, out of those significant 16 studies on sleep measures, patients were exposed to light in the morning in nine studies (1, 3, 4, 5, 6, 9, 10, 11, 16a), afternoon (16:00–20:00) in one study (7), both morning and afternoon in one study (12), evening in three studies (2, 14, 16b), and whole day in three studies (8, 13, 16c). The same relationship between duration of light exposure and illuminance levels can be observed for lighting interventions that improved sleep-related outcomes (Figure 3); however, no studies found significant improvements on sleep-related outcomes by short-term exposures to higher levels of illuminance (≥10,000 lux).

Illuminance and spectral qualities are important attributes of lighting environments, which not only determine the visual experience of patients but also impact circadian rhythmicity and therefore patients’ sleep, yet most of the articles did not provide detailed information about the lighting intervention’s spectral qualities. Out of all studies evaluated, only 1 reported the spectral power distribution of the lighting (Figueiro et al., 2014); 2 reported peak wavelength of the lighting (Lee et al., 2013; Royer et al., 2012); 4 reported color temperature; 10 articles reported minimal information such as full spectrum, white, or cool white; and the remaining 18 articles provided no information at all about the quality of the lighting. Future studies in lighting need to clearly identify and present the spectral quality of the light used.

Discussion

Based on results of the literature review, light interventions in healthcare settings can improve subjective measures of sleep quality, increase TST by 10–36 min, increase nocturnal sleep time by 1–1.7 hr, decrease the duration of daytime sleep by 18–66 min, decrease the number and duration of awakenings, increase sleep efficiency by 3.46–12.7%, reduce sleep onset latency by 1 hr, decrease sleep disturbances by 3.2 times, and decrease afternoon sleepiness. These myriad improvements in patient sleep outcomes by lighting interventions emphasize the importance of lighting systems in healthcare environments, yet the inconsistency of findings points to the need for further investigation of these systems.

These myriad improvements in patient sleep outcomes by lighting interventions emphasize the importance of lighting systems in healthcare environments, yet the inconsistency of findings points to the need for further investigation of these systems.

A combination of different aspects of lighting such as timing of exposure (morning, midday, evening), duration of exposure (30 min to whole day), illuminance (324 to higher than 10,000 lux), and spectral qualities determined effectiveness of lighting interventions in the reviewed studies. Short-term exposure (30–60 min) of high illuminance levels (≥10,000 lux), relatively long-term exposure (1–2 hr) of medium illuminance levels (3,000–10,000 lux), and long-term exposure (1–4 hr or whole day) to lower illuminance (≤3,000 lux), all can improve measures of patient sleep.

The evidence surrounding the impact of light on sleep-related factors is unequivocally positive, pointing to the high potential for effectively impacting the outcome of patient sleep. Although our literature review confirmed the effectiveness of light for improving patients’ sleep outcomes, the lack of consistent measurements and outcomes in the reviewed studies makes it difficult to compare and evaluate the relative effectiveness of lighting on sleep and sleep-related outcomes. While the heterogeneity regarding characteristics of subjects, settings, and care conditions associated with each effective light condition and the diversity of sleep variables, measurement methods, and tools does not allow us to make specific recommendations about the best possible lighting options, the finding of our literature review enables us to present a set of effective lighting conditions that can be implemented in developing alternative lighting systems and be tested through rigorous studies.

The majority of the studies in our sample are focused on elderly patients; only one article looked at nonelderly patients (Lee et al., 2013). Many of these studies (19 out of 34) have been done on sample groups of elderly patients who suffer from dementia. Aging itself is associated with sleep disturbances, and neurodegenerative diseases such as Alzheimer’s intensify sleep problems making it difficult to generalize the findings to other populations, such as healthier young patients in a hospital inpatient unit. More studies are needed to test the impact of lighting exposure in a hospital environment on improving sleep of younger adults as well as cognitively intact older adults.

The mechanism for delivering the lighting interventions in the studies in this review includes natural light exposure, light box, florescent lamps, LED luminaires, and light visors. Twelve studies delivered light through light boxes located in the middle of the rooms. Light boxes are more prevalent in lighting intervention studies, compared with more permanent architectural light fixtures such as wall or ceiling-mounted light sources. Future lighting studies should consider using lighting apparatus which are more typical of healthcare settings, such as ceiling-mounted lighting rather than light boxes to better allow for translation of the study findings to real-world lighting solutions.

Another common aspect of studies included in this literature review was the long intervention period from 1 week to 5 years. No studies evaluated lighting interventions for shorter than a week, which is a more typical length of stay for patients in inpatient units. Acute care patients have shorter lengths of stay but are critically ill and have more sleep deprivation and sleep disruption compared to patients on a general ward (BaHammam, 2006; Chan et al., 2012). Even if patients spend only three nights in a unit, the daily exposure of light could possibly impact their nighttime sleep. Future research should investigate the potential to improve patient sleep in acute care settings through lighting interventions.

Advances in understanding light and lighting technology have expanded our ability to both produce a great variety of lighting solutions and measure various aspects of that lighting. To be most helpful to the science of light and sleep, future studies should document the qualities of the lighting that are most important for influencing the sleep–wake rhythms, such as the spectral qualities and level of light that hits the cornea, as opposed to merely the ambient overall lighting levels. By discovering the right combination of lighting factors that are most effective at supporting good patient sleep conditions we can translate these findings into clear recommendations for designing healthcare environments. Designers need to evaluate different design parameters in terms of creating desired lighting levels. Building orientation determines the timing and duration of exposure to natural light in interior spaces. Glazing options such as window to wall ratio as well as internal and external shading options affect the quality of light penetrating into the space. Distance and angle of patient beds in relation to the exterior façade and windows also change the amount of light received at patient eye level. A combination of natural and artificial light solution should be considered in order to provide the desired light levels.

To be most helpful to the science of light and sleep, future studies should document the qualities of the lighting that are most important for influencing the sleep–wake rhythms, such as the spectral qualities and level of light that hits the cornea, as opposed to merely the ambient overall lighting levels.

Implications for Practice

Lighting in patient rooms needs to be designed with consideration of nonvisual responses to light, especially the impact that light has on patient sleep.

Designers need to consider the spectrum as well as intensity of lighting over the patient bed.

Controls need to allow for changes during the day so that a period of brighter light is possible for part of the day and lower light levels are possible in the evening hours.

Footnotes

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was funded in part by grants from Philips Lighting and Hill-Rom. It was conducted at SimTigrate Design lab, an interdisciplinary research lab dedicated to creating better healthcare experiences.

References

Akyar

Akdemir

(2013). The effect of light therapy on the sleep quality of the elderly: An intervention study. Australian Journal of Advanced Nursing (Online), 31(2), 31–38.

Ancoli-Israel

Gehrman

Martin

J. L.

Shochat

Marler

Corey-Bloom

Levi

(2003). Increased light exposure consolidates sleep and strengthens circadian rhythms in severe Alzheimer’s disease patients. Behavioral Sleep Medicine, 1(1), 22–36.

Ancoli-Israel

Martin

J. L.

Kripke

D. F.

Marler

Klauber

M. R.

(2002). Effect of light treatment on sleep and circadian rhythms in demented nursing home patients. Journal of the American Geriatrics Society, 50(2), 282–289.

BaHammam

(2006). Sleep in acute care units. Sleep and Breathing, 10(1), 6–15.

Chan

M.-C.

Spieth

P. M.

Quinn

Parotto

Zhang

Slutsky

A. S.

(2012). Circadian rhythms: From basic mechanisms to the intensive care unit. Critical Care Medicine, 40(1), 246.

Chong

M. S.

Tan

K. T.

Tay

Wong

Y. M.

Ancoli-Israel

(2013). Bright light therapy as part of a multicomponent management program improves sleep and functional outcomes in delirious older hospitalized adults. Clinical Interventions in Aging, 8, 565–572.

De Rui

Middleton

Sticca

Gatta

Amodio

Skene

Montagnese

(2015). Sleep and circadian rhythms in hospitalized patients with decompensated cirrhosis: effect of light therapy. Neurochemical Research, 40(2), 284–292.

Dowling

G. A.

Burr

R. L.

Van Someren

E. J. W.

Hubbard

E. M.

Luxenberg

J. S.

Mastick

Cooper

B. A.

(2008). Melatonin and bright-light treatment for rest-activity disruption in institutionalized patients with Alzheimer’s disease. Journal of the American Geriatrics Society, 56(2), 239–246.

Dowling

G. A.

Hubbard

E. M.

Mastick

Luxenberg

J. S.

Burr

R. L.

Van Someren

E. J. W.

(2005). Effect of morning bright light treatment for rest-activity disruption in institutionalized patients with severe Alzheimer’s disease. International Psychogeriatrics/IPA, 17(2), 221–236.

10.

Dowling

G. A.

Mastick

Hubbard

E. M.

Luxenberg

J. S.

Burr

R. L.

(2005). Effect of timed bright light treatment for rest-activity disruption in institutionalized patients with Alzheimer’s disease. International Journal of Geriatric Psychiatry, 20(8), 738–743.

11.

DuBose

J. R.

Hadi

(2016). Improving inpatient environments to support patient sleep. International Journal for Quality in Health Care, 28(5), 540–553.

12.

Evans

J. C.

French

D. G.

(1995). Sleep and healing in intensive care settings. Dimensions of Critical Care Nursing, 14(4), 189–199.

13.

Fetveit

Bjorvatn

(2004). The effects of bright-light therapy on actigraphical measured sleep last for several weeks post-treatment. A study in a nursing home population. Journal of Sleep Research, 13(2), 153–158.

14.

Fetveit

Bjorvatn

(2005). Bright-light treatment reduces actigraphic measured daytime sleep in nursing home patients with dementia—A pilot study. American Journal of Geriatric Psychiatry, 13(5), 420–423.

15.

Fetveit

Skjerve

Bjorvatn

(2003). Bright light treatment improves sleep in institutionalised elderly—An open trial. International Journal of Geriatric Psychiatry, 18(6), 520–526.

16.

Figueiro

Plitnick

Lok

Jones

Higgins

Hornick

Rea

(2014). Tailored lighting intervention improves measures of sleep, depression, and agitation in persons with Alzheimer’s disease and related dementia living in long-term care facilities. Clinical Interventions in Aging, 9, 1527.

17.

Figueiro

M. G.

(2008). A proposed 24h lighting scheme for older adults. Lighting Research & Technology, 40(2), 153–160.

18.

Gasio

P. F.

Kräuchi

Cajochen

Someren

E. v.

Amrhein

Pache

… Wirz-Justice

(2003). Dawn-dusk simulation light therapy of disturbed circadian rest-activity cycles in demented elderly. Experimental Gerontology, 38(1-2), 207–216.

19.

Hanford

Figueiro

(2013). Light therapy and Alzheimer’s disease and related dementia: Past, present, and future. Journal of Alzheimer’s Disease, 33(4), 913–922.

20.

Hood

Bruck

Kennedy

(2004). Determinants of sleep quality in the healthy aged: The role of physical, psychological, circadian and naturalistic light variables. Age & Ageing, 33(2), 159–165.

21.

Joshi

(2008). Nonpharmacologic therapy for insomnia in the elderly. Clinics in Geriatric Medicine, 24(1), 107–119.

22.

Kobayashi

Fukuda

Kohsaka

Sasamoto

Sakakibara

Koyama

… Koyama

. (2001). Effects of bright light at lunchtime on sleep of patients in a geriatric hospital I. Psychiatry and Clinical Neurosciences, 55(3), 287–289.

23.

Koyama

Matsubara

Nakano

(1999). Bright light treatment for sleep-wake disturbances in aged individuals with dementia. Psychiatry and Clinical Neurosciences, 53(2), 227–229.

24.

LaReau

Benson

Watcharotone

Manguba

(2008). Examining the feasibility of implementing specific nursing interventions to promote sleep in hospitalized elderly patients. Geriatric Nursing, 29(3), 197–206.

25.

Lee

S.-Y.

Aycock

D. M.

Moloney

M. F.

(2013). Bright light therapy to promote sleep in mothers of low-birth-weight infants a pilot study. Biological Research for Nursing, 15(4), 398–406.

26.

Lyketsos

C. G.

Veiel

L. L.

Baker

Steele

(1999). A randomized, controlled trial of bright light therapy for agitated behaviors in dementia patients residing in long-term care. International Journal of Geriatric Psychiatry, 14(7), 520–525.

27.

Martin

J. L.

Marler

M. R.

Harker

J. O.

Josephson

K. R.

Alessi

C. A.

(2007). A multicomponent nonpharmacological intervention improves activity rhythms among nursing home residents with disrupted sleep/wake patterns. Journals of Gerontology Series A-Biological Sciences and Medical Sciences, 62(1), 67–72.

28.

Mishima

Hishikawa

Okawa

(1998). Randomized, dim light controlled, crossover test of morning bright light therapy for rest-activity rhythm disorders in patients with vascular dementia and dementia of Alzheimer’s type. Chronobiology International, 15(6), 647–654.

29.

Mishima

Okawa

Hishikawa

Hozumi

Hori

Takahashi

(1994). Morning bright light therapy for sleep and behavior disorders in elderly patients with dementia. Acta Psychiatrica Scandinavica, 89(1), 1–7.

30.

Mishima

Okawa

Shimizu

Hishikawa

(2001). Diminished melatonin secretion in the elderly caused by insufficient environmental illumination. The Journal of Clinical Endocrinology and Metabolism, 86(1), 129–134.

31.

Okawa

Mishima

Hishikawa

Hozumi

Hori

Takahashi

(1991). Circadian rhythm disorders in sleep-waking and body temperature in elderly patients with dementia and their treatment. Sleep, 14(6), 478.

32.

Ouslander

J. G.

Connell

B. R.

Bliwise

D. L.

Endeshaw

Griffiths

Schnelle

J. F.

(2006). A nonpharmacological intervention to improve sleep in nursing home patients: Results of a controlled clinical trial. Journal of the American Geriatrics Society, 54(1), 38–47.

33.

Rea

M. S.

Bierman

Figueiro

M. G.

Bullough

J. D.

(2008). A new approach to understanding the impact of circadian disruption on human health. Journal of Circadian Rhythms, 6, 7.

34.

Rea

M. S.

Figueiro

M. G.

Bierman

Bullough

J. D.

(2010). Circadian light. Journal of Circadian Rhythms, 8(1), 2.

35.

Riemersma-van Der Lek

R. F.

Swaab

D. F.

Twisk

Hol

E. M.

Hoogendijk

W. J. G.

Van Someren

E. J. W.

(2008). Effect of bright light and melatonin on cognitive and noncognitive function in elderly residents of group care facilities—A randomized controlled trial. Jama-Journal of the American Medical Association, 299(22), 2642–2655.

36.

Royer

Ballentine

N. H.

Eslinger

P. J.

Houser

Mistrick

Behr

Rakos

(2012). Light therapy for seniors in long term care. Journal of the American Medical Directors Association, 13(2), 100–102.

37.

Satlin

Volicer

Ross

Herz

Campbell

(1992). Bright light treatment of behavioral and sleep disturbances in patients with Alzheimer’s disease. American Journal of Psychiatry, 149(8), 1028–1032.

38.

Schnelle

J. F.

Alessi

C. A.

Al-Samarrai

N. R.

Fricker

R. D.

Jr Ouslander

J. G.

(1999). The nursing home at night: Effects of an intervention on noise, light, and sleep. Journal of the American Geriatrics Society, 47(4), 430–438.

39.

Simons

K. S.

Laheij

R. J.

van den Boogaard

Moviat

M. A.

Paling

A. J.

Polderman

F. N.

… Pickkers

(2016). Dynamic light application therapy to reduce the incidence and duration of delirium in intensive-care patients: a randomised controlled trial. The Lancet Respiratory Medicine, 4(3), 194–202.

40.

Skjerve

Holsten

Aarsland

Bjorvatn

Nygaard

H. A.

Johansen

I. M.

(2004). Improvement in behavioral symptoms and advance of activity acrophase after short-term bright light treatment in severe dementia. Psychiatry and Clinical Neurosciences, 58(4), 343–347.

41.

Sloane

P. D.

Williams

C. S.

Mitchell

Preisser

J. S.

Wood

Barrick

A. L.

… Zimmerman

. (2007). High-intensity environmental light in dementia: Effect on sleep and activity. Journal of the American Geriatrics Society, 55(10), 1524–1533.

42.

Taguchi

Yano

Kido

(2007). Influence of bright light therapy on postoperative patients: a pilot study. Intensive & Critical Care Nursing: The Official Journal Of The British Association Of Critical Care Nurses, 23(5), 289–297.

43.

Ursin

(2002). Serotonin and sleep. Sleep Medicine Reviews, 6(1), 55–67.

44.

Van Someren

E. J.

Kessler

Mirmiran

Swaab

D. F.

(1997). Indirect bright light improves circadian rest-activity rhythm disturbances in demented patients. Biological Psychiatry, 41(9), 955–963.

45.

M. C.

Sung

H. C.

Lee

W. L.

Smith

G. D.

(2015). The effects of light therapy on depression and sleep disruption in older adults in a long-term care facility. International Journal of Nursing Practice, 21(5), 653–659.