Discomfort Glare

At low levels of glare people will often report annoyance rather than discomfort per se.  Although overall performance can be affected by this annoyance, generally visual performance will be unaffected.  At higher levels of glare physical discomfort is reported, rather than simply annoyance, and this can be accompanied by disablement (disability glare).

Many attempts have been made to find objective correlates of the discomfort (either as a way of evaluating discomfort glare or as a way of determining the mechanism underlying the discomfort) but there is no escaping the fact that the subjectivity of the discomfort makes one dependent upon the individual reporting their sensations. Probably the most startling finding from early research is that there are very large individual differences in responses to glare. Within the normal population there is a large variation in the discomfort reported by different people exposed to the same physical stimulus.  This range is further extended when people with clinical conditions, such as photophobia (an aversion to light) are included.

Furthermore, not only will different people report different amounts of discomfort for the same configuration of lights, but the same person will sometimes report different amounts of discomfort for the same light configuration at different times.

In general, discomfort can be reduced by reducing the contrast between the light source and the background (by either lowering the source luminance or by raising the background luminance), by reducing the size of the glare source, or by moving the glare source away from the line of sight.