Glare is the sensation produced by luminance(brightness) within the visual field that is sufficiently greater than the luminance to which the eyes are adapted to cause annoyance, discomfort, or loss in visual performance and visibility.
(IES, Illuminating Engineering Society of North America)
Blinding glare is so intense that for an appreciable length of time no object can be seen.
Direct glare is produced by poorly shielded luminaires, bright widows, or from reflecting areas of high luminance, such as a ceiling plane receiving the light output from an indirect luminaire that is only a few feet below the ceiling.
Disabling glare causes a reduction in visual performance.
Veiling glare is a disabling glare caused by extreme contrast within a task that prevents the viewer from properly seeing the task: for example, the reflection on a printed page made of coated paper. Someone looking down at the paper will have brightness reflecting from the glossy surface. Such veiling reflections on the paper surface cause loss of visibility.
Discomfort glare is an annoyance that does not necessarily prevent accurate seeing of a task but could affect a person's performance over a period of time by causing eye fatigue.
Reflected glare comes from reflections off highly polished or specular materials that can be viewed by an occupant.
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