Discomfort Glare and the Lighting of Buildings

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Abstract
Bright light sources can cause glaring effects which may impair visual efficiency. This may be brought about by a directly disabling effect, or it may result indirectly from irritation and discomfort. The purpose of the work described in the paper was to obtain more detailed knowledge of the effects of glaring light sources on comfortable vision. A technique of subjective appraisal was used, the basis of which was the control by the observer of a relevant physical variable to give in turn each of a series of precisely defined criteria of discomfort glare. It has been found that discomfort glare is primarily a function of the balance between the brightness and intensity of the glare source on the one hand, and the brightness of the surroundings on the other, the higher the brightness of the surroundings, the less discomfort will be caused by a given glare source. Due to the limited power of adaptation of the eye, the discomfort caused by large sources of high brightness may not, however, be capable of reduction by increasing the brightness of the surroundings. It has also been shown that small reductions in the brightness of large glare sources, such as windows, can result in a useful decrease in discomfort. The effect of the displacement of a glare source from the general direction of viewing, the effect of a change of brightness of the immediate surround to the source and the glare effect of a number of sources have been studied. The relationship between the various physical factors is complex, but the application of the results to problems of lighting design is readily made and is briefly discussed.

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