The Unified Glare Rating method (UGR) has been developed by the CIE (Commission International de l'Eclairage) in order to harmonise glare classification procedures worldwide. The method is based on a formula similar to that employed for the British Glare Index.
Unlike the Söllner Method, which simply evaluates Glare from a single luminaire, the UGR formula can be used to assess the glare characteristics of a complete lighting system. The formula takes account of every luminaire in a given interior and also background luminance (ceiling, walls) with reference to a standard viewing point.
A standard table is available listing uncorrected UGR values for various room sizes and reflectance combinations. These values have to be corrected to take account of such factors as the Luminous Flux of the light sources.
The final UGR scores tend to lie between 10 ("no glare") and 30 ("pronounced physiological glare").
The higher the UGR score, the greater the probability of glare. Completely different results can be achieved with luminaire locations that deviate from the standard configuration and for other viewing points. An auxiliary table provides estimated scores for the variant viewing points.
There are plans to lay down maximum UGR scores for various requirements and activities on the line of the glare quality classes used to date. The following table offers a rough conversion guide between the conventional DIN glare classes and the future UGR system.