Technical information
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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 experi-
enced with age as well as a reduction in the ability to adapt.
Glare can be divided into two dierent types; disability glare and
discomfort glare.
Sight impairment glare and discomfort glare can occur simulta-
neously or separately.
Light planning
EN 12464-1
Lowest shielding angle for the light source’s luminance
Light source’s luminance [kcd/m²] Minimum shielding angle
20 to < 50 15°
50 to < 500 20°
≥ 500 30°
The values in the table do not include indirect luminaires or luminaires that are
installed below normal eye level.
Calculation of the glare index
The degree of discomfort glare for indoor installations can be esti-
mated by calculating the glare index according to the UGR method.
The method will, through the introduction of the new standard
EN 12464-1, replace the previous European calculation method
(NB-method). The demands on the glare index documented in
EN 12464-1 refer to the highest average value for the lighting. The
UGR-method (Unified Glare Rating) is described in CIE’s publication
no 117-1995.
The UGR glare index for discomfort glare is ranked on a scale,
which in practice runs from 13 to 28 where the higher the glare
index the higher the level of glare. The smallest change in the glare
index denoting a significant dierence is 3.
The glare number should be calculated according to the ‘table
method’ to check whether the recommended glare index in the
standard’s tables is met by a specific lighting installation. (The
method is described in CIE’s publication no 117-1995). However, this
method assumes that the luminaires in the room are positioned
symmetrically and feature symmetrical light distribution across and
along the luminaire.
Luminaire manufacturers provide information/table data as a
part of the luminaire’s photometric data to calculate the lighting
installation’s glare index.
Disability glare
Disability glare usually occurs when an object in the vicinity of the
normal line of sight, has a significantly higher luminosity or lumi-
nance 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
aected negatively and cause deterioration in visibility, or what is
known as contrast reduction.
This contrast reduction can be sucient to make words and
images barely visible and in doing so make it dicult 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 eectively shield the light source (see table).
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