Lighting Research & Technology

The dynamic control of daylight is seen as key for the effective exploitation of natural illumination in buildings. Traditional control solutions are invariably used in a sub-optimal manner: blinds/shades are left down for long periods and lights are left switched on. A glazing with a transmissivity that varies continuously between clear and dark extremes, and which can be controlled automatically, could be much more effective in providing a ‘well-tempered’ daylit environment that meets occupants needs. Amongst the different types of variable transmission glazing that have undergone extensive research and development in the last few decades, those based on electrochromism appear to have the best performance characteristics and the greatest market potential. Electrochromic (EC) glazing generally exhibits a shift in spectral transmission as the glass darkens, e.g. causing it to appear blue as it tints. Occupants, however, are believed to prefer a neutral spectrum of daylight illumination without any pronounced hue. In this paper, the authors show that it is possible to maintain a neutral spectrum of illumination with electrochromic (EC) glazing under normal operation provided that just a small proportion of the EC glazing is kept in the clear state. A theoretical model to predict the daylight spectrum resulting from any arbitrary combination of clear and tinted glazing is described. Predictions from the model are compared with measurements of the daylight spectra in an office with EC glazing under various states of tint. The predicted spectra show excellent agreement with the measurements. The model is applicable to any combination of clear and/or tinted glass panels irrespective of the glazing type(s). The paper concludes with a discussion of design considerations for the effective deployment of EC glazing.

This paper provides recommendations for optimum LED light spectra in shop environments. The main aspects of the research were to elaborate the optimal LED spectral power distribution for the lighting of different colour textiles, fruits and vegetables, meat and bakery products. The spectrum was tailored towards different colour quality metrics such as the colour rendering index and the colour quality scale. Small scale investigations with eye-tracker studies were carried out by Osram Opto Semiconductors at the University of Regensburg and full scale experiments were conducted at the University of Pannonia during the project in order to determine which metric correlates best to the preference of the observers. Results of the psychophysical have been evaluated with the help of analytic hierarchy process and a modified Thurstone method. As a result of the investigation, optimal spectral power distributions for shop environment are described.

International organizations have proposed laws, regulations and standards to control light pollution. Korea enacted the Light Pollution Prevention Act on 2 February 2013. This Act designates ‘the luminous environmental zone’ through ‘the luminous environmental impact assessment’ and restricts light emission in the designated area according to the related light emission standards. This paper proposes a quantitative assessment methodology for the luminous environmental impact assessment. For decorative and advertisement lighting, a method using minimum field measurement is suggested. For street lighting, the total emitted luminous flux density is calculated based on security lighting data. Based on such data, a determination is made as to whether a luminous environmental zone for a particular area should be designated or not.

Past studies have shown that the Feeling of Contrast Index (FCI) correlates with preference in some circumstances, but the exact relationship is not clear and may differ among visual conditions and targets. This paper presents a psychophysical experiment in which 70 observers evaluated the colour quality of natural objects under different spectral power distributions with different values of FCI but the same correlated colour temperature (3000 and 5000 K). Results show that FCI holds a nearly perfect linear correlation with vividness (r = 0.976); unnaturalness associated with enhanced vividness rendered by excessively high FCI deteriorates preference. These effects are independent of correlated colour temperatures, but are dependent upon the visual targets used because of limitations in the derivation of FCI. Compared to other metrics, FCI can characterise vividness under a light source.

One of the crucial street lighting design steps considerably influencing electricity consumption is the selection of an appropriate lighting class. Therefore, after a detailed analysis of the current CEN and CIE selection procedures for streets and roads with motor or mixed traffic, several modifications of the CIE 115-2010 procedure are proposed. This way not only is its simplicity maintained but also the agreement between the two procedures is increased by up to 50%. The modifications are related to the weighting values corresponding to the traffic composition and ambient luminance as well as the inclusion of a value linked to the complexity of the visual field. The necessity for further investigation regarding the selection of lower lighting classes during the late night hours and the determination of appropriate luminance levels is also discussed.

Lighting design for office buildings has focused largely on providing sufficient light for visual performance, minimal glare, good colour rendering and energy conservation. Little attention has been given to understanding how light affects the non-visual systems, including circadian regulation that affects sleep and mood. Circadian light–dark and activity–rest patterns of individuals working in a building designed to provide daylight availability in the space were obtained in winter and summer. Measures of objective and subjective sleep and self-reports of mood were also obtained from participants. Results show a significant increase in light exposure during summer. Sleep quantity and quality were also significantly higher in summer than in winter. Strategies to increase circadian light exposures in buildings should be a consideration in architectural design.

We propose a method for the design of a freeform reflector by means of feedback methods to create light-emitting diode (LED) sources with uniform illuminance. A reflector is first designed to obtain a uniform circular light distribution for a point source. Then the optical performance of the reflector is investigated for both the point sources and extended sources based on a Monte Carlo ray tracing method. Comparing the illumination differences, a new reflector is generated by adding feedback. Repeated iterations of feedback can improve the reflector performance. To validate the method, a reflector is designed for an extended LED source. The results demonstrate that the illuminance uniformity can reach 88% and system efficiency can reach 97.4% simultaneously, after six feedback cycles. These are certainly able to meet the needs of general lighting applications.

Based on the edge-ray principle of non-imaging optics, an optical design method for a lens producing small angle, uniform illumination from a high-power light-emitting diode light source has been developed. The energy correspondence between the light-emitting diode light source and the illuminance distribution on a target plane was established, and a number of discrete points for freeform profile curves which could achieve uniform illumination over a small angle were calculated and fitted to create a lens. Finally, simulations were performed using software. The influence of the size of light source on the emitting angle under uniform illumination was also investigated. The results show that the optical system can achieve uniform illumination with an extended source, the divergence angle being controlled within a minimum range by the optical design method.

Cuttle has proposed mean room surface exitance as a metric for use within interior lighting design. Two reported barriers to its use are: a lack of available software to calculate the metric and the tedious and cumbersome nature of recording its values in the field using current equipment and methodologies. This paper presents a method for facilitating the calculation of mean room surface exitance using readily available freeware, namely Radiance, and also presents a methodology that utilises high dynamic range imaging as a pragmatic alternative for field measurement.