Daylight Glare Index (DGI)

The IES glare index system is based on a glare constant which can be derived for each light fitting using the BRS glare formula.

DGI daylight glare index
source luminance in cd/m²
average background luminance in cd/m²
angular size of the source in steradians as seen by the eye
solid angle subtended by the source,modified for the effect of the position of the observer in relation to the source in steradians
Zone Region DGI UGR
Discomfort zone intolerable >28 >28
just intolerable 28 28
uncomfortable 26 25
just uncomfortable 24 22
Comfort zone acceptable 22 19
just acceptable 20 16
noticeable 18 13
just perceptible 16 10
Glare regions and their related glare index

The DGI is related to the IES glare index scale as follows:

DGI = 2/3 (IES glare index + 14)