Lighting Research & Technology

In order to evaluate the circadian effects of light, an approach based only on a circadian sensitivity function makes it possible to easily obtain efficiency functions and action factors. However, it does not take into account the circadian human response to light stimuli, which is not linear. Non-linear models are more sophisticated and accurate but they are not easy to apply. In this paper a proposal for an easy way to evaluate the potential ‘circadian effects’ of light sources is presented. Although the model is quite simple, results are in good agreement with those obtained by means of one of the most accurate non-linear models.

Two studies were designed to investigate the carryover effects of daylight on performance and self-reports of sleepiness. The effects of daylight and of darkness were compared independent of the effects of simultaneous periodic, 1-hour exposures to narrow-band blue and red lights over the course of 26-hour sessions. Nighttime performance on a 54-minute tracking task, but not subjective sleepiness, was significantly better following exposure to daylight. There was no differential effect on performance or sleepiness from exposure to the blue or red lights. Eight of the participants returned to experience a completely dark session and a replication of the daylight and intermittent blue light session. Nighttime performance and subjective sleepiness were significantly worse for the dark session than for daylight-plus-blue sessions in both studies.

CIE 191:2010 recommends a mesopic photometry system that defines the luminous efficiency function for peripheral visual tasks, which vary depending on the adaptation state of observers. For implementation of the system, an adaptation field to determine the adaptation state needs to be defined. To address this issue, vision experiments have been conducted to measure surrounding luminance effects on the adaptation state at a peripheral task point. The results reveal that the adaptation state depends mainly on the local luminance at the task point but there is also a small effect of the surrounding luminance. The results suggest that the surrounding luminance effect is larger than the veiling luminance predicted with existing foveal models; nevertheless, it is not significant for the mesopic luminance on uniform luminance distributions.

In this paper, a natural lighting system composed of a tilted prismatic daylight collector, an outdoor reflector and an indoor diffuse reflector is described. The light emerging from the hypotenuse of the prismatic daylight collector is redirected onto the indoor reflector for natural light illumination. The results of measured illuminances are in agreement with the results of calculation. The prismatic daylight collector not only decreases discomfort glare but also collects daylight for the natural lighting system. The open natural lighting system, which uses less material, can be realized by the detailed analysis of the characteristics of the light emerging from the hypotenuse of the prismatic daylight collector for sunlight incident on the collector.

This study proposes a supplementary lighting and regulatory scheme for application in semi-closed crop production systems. This supplementary lighting control module is primarily based on fuzzy logic inference and an expert database. Under the hypothesis that the temperature and humidity conditions are consistent, the system will implement supplementary lighting of different wavelengths according to current solar spectral distribution conditions and plant growth patterns. Simulations demonstrate that under the condition of full sunlight, the system still provides supplementary light to compensate for insufficient light spectrum. Compared to traditional plant lamps that need to be lit for long periods of time, this system can randomly adjust light spectrum and intensity to achieve energy savings, and is therefore suitable for application in lighting control systems in future greenhouses.

High-power integrated LEDs usually have a bright square surface. When the rays emitted from them are collected to project a round spot at a very short distance using a rotationally symmetrical reflector, there will be a dark spot in the centre. This problem can be avoided in advanced lighting systems. A discontinuous surface reflector is designed by a simple method based on the three-dimensional form of compound parabolic concentrators. The dark spot is removed, and the uniformity is better.

The increase in the LED junction temperature is an important problem since it directly affects the lumen output and the colour characteristics of the LED chips, resulting in low performance in LED-based lighting systems. In this study, commercial computational fluid dynamics software is used with the JEDEC’s two-resistor compact thermal model to analyse the temperature distribution in two selected luminaires. It is aimed to show that use of the two-resistor model and measurement combination is a fast and easy way of predicting thermal behaviour of the system and LED junction temperatures instead of trial and error designs and thus ensures a better estimation for the total luminous flux of the luminaire and lowers the costs and time required for the prototyping processes.

This study is based on a general interior lighting installation and discusses the relation between veiling luminance and the unified glare rating. Through curve fitting and a derived formula, a transfer function between veiling luminance and the unified glare rating is generated. This result connects disability glare and discomfort glare within a finite range, where the relation between them is almost linearly dependent. This transfer function has a high accuracy as shown by a comparison between the calculated results and the original data, and is the first to provide a connection between disability glare and discomfort glare.

Smart lighting is used to provide the right light to meet occupants’ needs for efficiency, productivity and health. The development of adaptive control in smart lighting requires advanced real-time sensing technologies for monitoring the generated light field. This paper introduces a systematic approach to dynamic light field sampling using a distributed sensor network. A dynamic adaptive sampling algorithm is introduced to guide the adaptive selection and real-time reallocation of sample locations to track and estimate the generated light field and the daylight field. This approach generates a multi-scale functional representation of the light field, which can be an effective basis for lighting control. Experimental results have shown that a systematic dynamic selection of sensor locations can significantly reduce the error in representation of the light field with corresponding improvement in the lighting control.