What Is Glare?
Glare is a visual sensation caused by excessive and uncontrolled brightness. It can be disabling or simply uncomfortable. It is subjective, and sensitivity to glare can vary widely. Older people are usually more sensitive to glare due to the aging characteristics of the eye.
Disability glare is the reduction in visibility caused by intense light sources in the field of view, while discomfort glare is the sensation of annoyance or even pain induced by overly bright sources.
What Causes Glare?
When light is scattered it causes a ‘veil’ of high luminance over the retina = reducing contrast.
A great example of this is when you face high-beam headlights when everything else around you is dark.
There are four factors involved when assessing Glare?
Luminance of source (Luminance -the surface brightness of an object measured in candelas/m²)
Luminance of Background
Size of Glare Source
Position of Glare source
How is Glare calculated?
‘The rating of discomfort glare shall be determined using the CIE (International Commission on Illumination) Unified Glare Rating (UGR)’. EN 12464-1:2011 Light and Lighting of Work places
(UGR) tabular method. Variations of UGR can be determined using the comprehensive tables for different observer positions, as detailed in report CIE 117-1995
CIE 117-1995 calculates a table of glare indices for a regular grid of luminaires based on a set spacing using the following formula :
How Does UGR relate to Discomfort Glare?
The UGR rating helps to determine how likely a luminaire is to cause discomfort to those around it. For example, the discomfort that a LED Panel will cause the workforce within an office