Following the introduction of the latest EN 12464-1, UGR will replace the previous European calculation method (NB-method). The demands on the glare index documented in EN 12464-1 refer to the highest average value for the lighting. The UGR-method (Unified Glare Rating) is described in CIE’s publication no 117-1995.
The UGR glare index for discomfort glare is ranked on a scale, which in practice runs from 13 to 28 where the higher the glare index the higher the level of glare. The smallest change in the glare index denoting a significant difference is 3.
The glare number should be calculated according to the ‘table method’ to check whether the recommended glare index in the standard’s tables is met by a specific lighting installation. (The method is described in CIE’s publication no 117-1995). However, this method assumes that the luminaires in the room are positioned symmetrically and feature symmetrical light distribution across and along the luminaire.
Luminaire manufacturers provide information/table data as a part of the luminaire’s photometric data to calculate the lighting installation’s glare index.