Glare is the word given to a problematical distribution of luminance and/or excessive luminance contrast in the field of vision which causes disturbed vision. Glare is divided into two types depending on its effect:
Glare that causes a loss of visual performance (e.g. reduced perception of shapes and capacity for discrimination caused by glare from the headlights of an approaching car at night).
Glare can be caused in one of two ways:
Glare originating directly at the light source. The degree of direct glare depends on the size and luminance of the visible luminous areas of all the luminaires in the field of vision and also on background luminance. Direct glare is considered adequately controlled where the mean luminance of the luminaires at the critical emission angle of 45°-85° does not exceed the values of the luminance limiting curves.
Glare and loss of contrast caused by reflections from luminous objects (e.g. on glossy paper or computer screens). In general, reflections lead to reduced contrast perception, which hinders character recognition on printed paper, for example. Reflected glare can be avoided or reduced by the following means:
Careful planning of the relative positions of luminaires and workstations
- The use of luminaires with an appropriate luminance limit angle to avoid
reflections in the working surface or object
The use of matt, diffuse or reflection-reduced surfaces at the workstation
Diffuse light control with systems offering a high proportion of indirect light or vertical illuminance