Determining the glare effect of a light source or a group of light sources is complicated. Glare will certainly increase as the number and size of light (or glare) sources increases. The size, luminance and position of light sources will all affect the level of glare experienced.
Glare is subjective but can be evaluated using a system devised for outdoor sports applications by the International Commission on Illumination (CIE) on the basis of extensive field tests. The CIE 112-1994 Glare Evaluation System for Use within Outdoor and Area Lighting – defines a glare rating (RG) with an assessment scale of 10 to 90. The lower the glare rating, the better.
The validity of this system is restricted to viewing directions below eye level, and it is mainly used for predicting the degree of glare. The lighting design phase should include a glare assessment based on the CIE 112-1994 Glare Evaluation System for Use within Outdoor and Area Lighting. Calculations should be made for observer positions at each of the 96 UEFA reference grid points. Assessments should be made every 15°, starting from 0° or 180°, over a total 360°. Observer positions should be 1.75m above the pitch surface.
The maximum glare rating and the corresponding direction should be recorded for each observer position.