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

licht.wissen 01
Lighting with Artificial Light
Lighting technology – Parameters and terms
Illuminance, luminous efficacy, maintenance factor. Planning a lighting system requires knowledge of the basic
terms and parameters of lighting technology.
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Luminous flux
The luminous flux indicates how much light
a light source emits in all directions. It describes
the overall light output and is measured
in lumens (lm).
The luminous flux is determined using special
measuring devices or calculated mathematically.
It is an indicator of the total
brightness V () of a luminaire as perceived
by the human eye. DIN 5031-1 provides a
virtual average in the form of the V-lambda
curve.
In the era of efficient LEDs, the lumen rating
is increasingly replacing the wattage which
was used in the past to indicate the brightness
of a light bulb. In lighting design, the
luminous flux of a luminaire (in contrast to
the luminous flux of the lamp) includes
losses arising from the luminaire design.
Luminous intensity I
In order to calculate the distribution of light
in a lighting system, it is not sufficient only
to know the luminous flux; the distribution
of the luminous flux in a particular angle
must also be known. The luminous intensity
is therefore the part of the luminous flux
which radiates in a certain direction. It is
measured in candelas (cd).
The luminous intensity distribution of reflector
lamps and luminaires is shown in a polar
diagram (luminous intensity distribution
curves, IDCs).
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Illuminance E
Illuminance () describes how much light
falls on a surface. The quotient of the luminous
flux (= ) and the illuminated surface
(= ) is determined for this: = /. The
unit for illuminance is lumen per square
metre; it is given in lux (lx).
The illuminance can be calculated for any
virtual plane in space or can simply be
measured using a lux meter. In offices the
working plane, e.g. the desk, is horizontal –
light technicians speak here of a horizontal
illumination area. In the case of shelving
units or for facial recognition, on the other
hand, vertical illumination is of importance.
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Luminance L
Luminance can be perceived by the eye.
It describes the impression of a surface’s
brightness as dictated by its colour and
material. The unit of luminance is cd/m 2 .
Luminance is used in outdoor lighting as a
planning factor. For fully diffuse reflecting
indoor surfaces, the luminance can be calculated
in cd/m 2 from the illuminance in
lux and the reflectance :
L = · E
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