About glare

Glare occurs when part of an interior space is significantly brighter than the room’s luminosity. In these instances the eyes are exposed to a more intense light than they are normally adapted to. The most common cause of glare occurs when the luminaire and window can be seen directly or via reflections, within the normal field of vision.

Elderly people are usually more irritated by glare than young people. This is mainly due to the increased clouding of the eyes lens experienced with age as well as a reduction in the ability to adapt.

Glare can be divided into two different types; disability glare and discomfort glare.

Sight impairment glare and discomfort glare can occur simultaneously or separately.

Disability glare

Disability glare usually occurs when an object in the vicinity of the normal line of sight, has a significantly higher luminosity or luminance than that which usually occurs in the field of vision. If an eye is exposed to a continuous intense light, the eye’s adaptation can be affected negatively and cause deterioration in visibility, or what is known as contrast reduction.

This contrast reduction can be sufficient to make words and images barely visible and in doing so make it difficult to carry out the visual task. Alternatively, if the light source causing the glare is directly in the line of sight this can cause noticeable after-images. The most common source of sight impairment glare internally, is the sun and sky viewed from a window or a badly shielded light source observed directly or via reflection.

Disability glare should therefore be prevented through using luminaires that effectively shield the light source (see table).

Lowest shielding angle for the light source’s luminance

Light source’s luminance [kcd/m²]
Minimum shielding angle
20 till < 50 15°
50 till < 500 20°
≥ 500 30°
The values in the table do not include indirect luminaires or luminaires that are installed below normal eye level.