Technical information

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Light planning
EN 12464-1
Discomfort glare from electric light
Discomfort glare is an immediate occurrence and arises from light
sources or luminaires whose luminance is greater than the eye can
adapt to, but can also become noticeable after a period of time.
The degree of discomfort glare, depends on several factors; the
luminance and the size of the glare source, the position of the glare
source in relation to the line of sight and the background luminance
against which the glare source is viewed.
Consequently, when light planning the luminaire’s luminance
should always be considered in relation to the background lumi-
nance. The closer the dazzling surface is to the eye, the greater the
risk of discomfort glare. In open luminaires, especially those for
compact and other intense light sources with high luminous flux, it
is generally the light source itself or a mirror image in the specular
reflector that causes the glare eect. One way to reduce discomfort
glare is to use satin matt reflectors and luminaires with a larger
surface area.
Discomfort glare can also be reduced by increasing the luminos-
ity on walls and ceiling of a room. This can be achieved in dierent
ways:
Using luminaires with an uplight component. •
Positioning the luminaire closer to the walls in the room. •
The walls can be lit separately or the luminosity increased by •
choosing higher reflection factors on the wall surfaces.
Walls that appear brighter in relation to the visual object can create
adaptation problems. The luminosity of the room surfaces should
therefore be adapted to the visual conditions and be limited as
described in the Luminance distribution and luminance limitations
chapter.
Discomfort glare from windows
An awkward and unpleasant glare arises when a person looks out
of a window in the direction of the sun, or when direct sunlight falls
against surfaces within the normal field of vision. In these situa-
tions even discomfort in the form of increased heat radiation can
also occur. Thus sun screening in some form is necessary in most
buildings.
Screening can be achieved through the design of the building,
external sun screens, low transmitting glass (sun glass windows) or
through Venetian blinds or curtains. Glare can also occur from a dif-
fuse sky viewed through a window. This form of glare can usually be
reduced by choosing lighter colours for the walls near the window
or by increasing the luminosity of the walls with separate lighting.
Examples of discomfort glare from a window:
Reflective glare.•
Reflections on visual objects or their surroundings can completely •
impair sight.
Even if glare does not occur from a luminaire or other highly
reflective surfaces, it can occur in the form of reflection. Polished
and reflective materials should not be placed in areas where glare
can arise, especially in work areas. If polished surfaces cannot be
avoided lighter surfaces are more preferable than darker surfaces.
An example is a computer monitor screen surface where reflections
are usually perceived as more disturbing on monitors with dark
backgrounds and light text, than on monitors with light back-
grounds and dark text.
Reflections from reflective materials or reflective glare can usually
be prevented with the following actions:
Suitable luminaire positioning.•
Selecting luminaires with low luminous intensity and eective •
screening.
Selecting matt materials for reflective surfaces.•
Selecting luminaires with a larger surface area.•
Select light colours for ceilings and walls.•
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