licht.wissen 19 No. "Impact of Light on Human Beings"

oom use in mind. To ensure that they have
a biological effect and that undesirable
flicker effects do not occur, they should
take at least several minutes to complete.
In the evening, light with an activating effect
should generally be avoided. This is to prevent
interference with melatonin production
and prepare the body for sleep. DIN SPEC
67600 recommends the use <strong>of</strong> dimmed, directional
light in warm light colours with a
higher red and sharply reduced blue content
for around two hours before going to
bed.
Shift work
For people who work shifts, the requirements
that need to be met by melanopically
effective lighting are very complex. A shiftworker’s
circadian rhythm is <strong>of</strong>ten different
from the sleep/wake rhythm that nature intended.
Hence the call by chronobiologists
for shift work models that are less disruptive
for the human biological clock. DIN
SPEC 67600 contains proposals for supportive
lighting.
Material characteristics and light colour
The designer <strong>of</strong> a circadian-effective lighting
installation must also ensure that the
spectrum radiated by a light source is not
distorted, either by the luminaire or by ambient
colours in the room.
Lamp light is altered in luminaires, especially
by optical control elements such as
louvers, enclosures or prisms. This may result
in the light that reaches the eye having
a different spectral composition than that
radiated by the lamp. The spectral properties
<strong>of</strong> optical control elements determine
the quality <strong>of</strong> dynamic lighting. In the worst
event, the colour temperature <strong>of</strong> an 8,000
kelvin lamp can be lowered to just 6,500
kelvin in the room.
Room environment and light colour
Visual atmosphere is influenced significantly
not only by the light colour <strong>of</strong> the light
sources used but also by the colours <strong>of</strong> furniture,
walls and ceiling. Dark colours reflect
less light than light ones. A great deal
<strong>of</strong> light can be “lost” here, especially where
light is cast exclusively onto room surfaces
by indirect luminaires. Wood finishes, reds
and browns as well as opalescent furnishing
elements absorb the blue content <strong>of</strong> the
spectrum and thus considerably reduce the
biological effect <strong>of</strong> lighting.
[41] Our internal clock is best synchronised
by artificial light in the morning. Higher illuminance
on ceiling and upper walls, a higher
blue content and planar light distribution are
recommended to ensure that the right photoreceptors
are reached.
[42] Towards evening, the body is prepared
for rest: lighting should be geared only to the
performance <strong>of</strong> visual tasks, delivering directional
light with a minimum blue content.
[43] Biologically effective lighting supports
circadian rhythms with dynamic changes in
light colour and illuminance.
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