1. excessive luminance values in the field of view
2. too high luminance contrasts
Windows can have a high luminance compared with other luminances in a room. This gives a strong contrast from inside to outside, potentially causing glare. In Radiance simulations we may offset this by providing some internal background lighting. The strongest luminance source is the Sun, and if this in the field of view then glare is inevitable. The default glare threshold is calculated by the program to be 7 times the average luminance level, if required the user can specify an alternative value.
We normally give the CIE Glare Index and the GUTH Visual Comfort Probability (% of people who are satisfied) as measures of glare. These values are calculated at fixed angles to the left and right of the centre of focus (usually at 10 degree intervals from –60 to +60 degrees), see figure below.
