A study on overhead glare in office lighting conditions

Abstract

Abstract— High‐intensity light sources illuminating the human eye may create discomfort glare, or at higher intensities even disability glare. In many office lighting conditions, light from overhead luminaires in the ceiling may deliver stray light into human eyes, and as such create discomfort glare, generally referred to as overhead glare. In this paper, overhead glare for a LED luminaire comprising a matrix array of small LED sources using subjective evaluation methodologies and theoretical models, commonly accepted to evaluate glare, were investigated. The perceived overhead glare of the LED luminaire is evaluated at various luminance levels and at different angles (i.e., between 55 and 90°) with respect to the line of sight of the viewer. The results show that a luminaire comprising a matrix of high‐intensity point sources can cause overhead glare and can become glary at lower averaged luminance levels than a luminaire with a uniform light source even at high evaluation angles with respect to the line of sight of the viewer. In addition, the conventional UGR model for predicting discomfort glare needs adaptation for a reliable prediction of perceived overhead glare of complex LED luminaires consisting of a matrix of small‐sized high‐intensity light sources.

50.4: Relation between Short‐term and Long‐term Assessment of Glare

“…The glare rating was used as dependent variable, the luminance level (5 levels) as fixed factor, and the subjects as random factor. As could be expected from existing literature [2, [4][5]7], the result showed a statistically significant effect of luminance level on perceived discomfort glare (p<0.001). The perceived glare logarithmically increased with the luminance (r2=0.99), as shown in Fig.1.…”

“…The LED luminaires used were specifically built by Philips Lighting, and were also used in the research by Xia et al [7]; they consisted of a 7x7 array of LEDs, but contrary to their previous use the LEDs now were covered with diffusers with 90% light transmissivity. The average luminance of the exit window was controlled by a Dali (Digital Addressable Lighting interface) controller between 1148 cd/m2 and 4842 cd/m2.…”

“…In addition, the effect of spatial frequency on perceived discomfort glare becomes more pronounced as the position of the luminaire is closer to the line of sight. Xia et al [7] studied discomfort glare in an office, and evaluated a point array LED luminaire at various luminance levels and angles with the line of sight (i.e., between 55°and 90°). Their results clearly showed that the point array LED luminaire generated more discomfort glare at higher luminance levels even at angles with the line of sight as high as from 55° to 90°.…”

Systematic review on the interaction between office light conditions and occupational health: Elucidating gaps and methodological issues

“…Geerdinck et al 43 found, based on acceptance scores, that luminaires with non-uniform luminance patterns provoke more discomfort glare than uniform light sources in office landscapes. Xia et al 50 agreed with Geerdinck et al 43 and highlighted, based on their repeated measures design, that the luminance level of the exit window of the LED luminaire has a significant effect on perceived overhead glare. Hirning et al 48 investigated discomfort glare in a field study.…”

P‐142: Influence of Illumination Level on Visual Fatigue and Lighting Preference for Different Age Groups in China

“…However, as with any new technology, it can have some unwanted properties that were absent or less dominant for the conventional, wellestablished, lighting technologies. In particular, the high intensity of individual LEDs and their non-uniform luminance distribution in a luminaire can give rise to discomfort glare, which eventually could induce serious visual fatigue [1]. The widely used Unified Glare Rating [2] does not always correctly predict the degree of experienced discomfort glare for these particular LED-based luminaires.…”