1. Excessive luminance values in the field of view.
2. Excessive luminance contrasts.
Windows can have a high luminance compared with other luminances in a space. This can create a high contrast within a space, potentially causing glare. In RadianceIES simulations, this may be offset 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 defined by RadianceIES to be 7 times the average luminance level. If required, the user can specify an alternative value.
The CIE Glare Index and the Guth Visual Comfort Probability (percentage of people who are satisfied) are the most commonly used glare metrics. 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.
