licht.wissen No. 01 "Lighting with Artificial Light"

licht.wissen 01
Lighting with Artificial Light
Harmonious distribution of brightness
Excessive brightness differences are visually tiring and reduce the sense of well-being because the eyes are
constantly required to adapt. But just as unpleasant as excessive contrasts are negligible differences in luminance
which can quickly make a room appear monotonous.
[39] The illuminance in a space reveals
nothing about the harmonious distribution of
brightness. This is only apparent from the luminance
values (cd/m 2 ) as shown in this example.
[40] Roads, too, should be uniformly and
thus “safely” lit. This is not necessarily “monotonous”.
The best solution is a harmoniously balanced
distribution of brightness in which
the luminance (symbol: L) of visual objects
allows them to be clearly distinguished and
differentiated against their background.
With regard to safety, DIN EN 13201 requires
uniform illumination of the road surfaces
of thoroughfares and the avoidance
of dark zones. Major differences in brightness
should also be avoided indoors; this
allows any hazards to be spotted in good
time, e.g. in industrial facilities. Accordingly
the European standard DIN EN 12464-1
also recommends a balanced distribution
of luminance levels which significantly aids
visual performance and visual comfort in
indoor work places.
Balanced luminance levels
In order to achieve this, the luminance
levels of all surfaces must be considered.
These are determined by the reflectance
and the illuminance of the surfaces.
Recommended reflectance levels according
to DIN EN 12464-1 (see also fig. 23,
page 16):
Ceiling: 0.7 to 0.9
Walls: 0.5 to 0.8
Floor: 0.2 to 0.4
It should also be ensured that the luminance
ratio between the work area and the
immediate surroundings does not exceed
3:1. The luminance ratio between the work
area and more distant areas should not
exceed 10:1.
In offices, for example, lighting which is
coordinated with the colours and surfaces
of the interior helps ensure harmonious
brightness distribution. Key criteria here
include:
Dedicated lighting for a particular work
place or room
Uniform illuminance on a surface (= U O as
the ratio of minimum to average illuminance),
as required by DIN EN 12464-1.
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