Photometric parameters Luminosity
Cut-off angle
Formula symbol:
I
Formula symbol:
q
Unit:
cd
Unit:
°
q
The luminous flux radiated by the illuminant spreads into the room at
The cut-off angle of a luminaire is defined according to DIN EN 12464-1
a certain angle. The luminous flux divided by this room angle produces
”Lighting of indoor workplaces” as the angle between the horizontal
the luminosity I. Since most light sources radiate the light at different
plane (usually also mounting surface) and the direction from which the
intensities in different directions, the distribution of luminosity in all
lamps and the surfaces of high luminance cease to become visible. If
directions needs to be given to fully describe the light field. The repre-
the correct cut-off angle is not observed, there is a danger with direct
sentation of a plane in a polar coordinate diagram is called a luminosity
beam luminaires of direct glare from excessive luminance.
distribution curve (LDC).
Luminance at y = 65° Formula symbol:
L
Unit:
cd/m2
Half-Peak Spread
γ = 65°
γ = 65°
Formula symbol:
a
Unit:
°
E 2
15°
max
γ = 0°
E
max
γ = 0°
High luminance upwards of an angle of = 65° can directly and
With spotlights and reflector lamps the half-peak spread is
indirectly (e.g. via reflection off a screen) create annoying glare.
given as a photometric value. This is the angle at which the luminosity
Therefore the luminance between 65° and 85° must not exceed
of the spotlight has decreased to half the maximum luminosity.
stipulated limits.
Luminous flux
Lighting Strength
Formula symbol:
F
Formula symbol:
E
Unit:
lm
Unit:
lx
The radiative flux radiated by a light source (illuminant), assessed
The luminous flux striking an area at any inclination, divided by
according to the spectral luminous efficacy v (lambda) stipulated by
this area, is called the illuminance. It is the assessment value for the
the International Commission on Illumination (CIE), is called luminous
illumination level, e.g. of a working area or a room (see also DIN EN
flux. The nominal luminous fluxes of illuminants should be taken from
12464-1). The illuminance is represented by means of isolux curves.
the documentation of the respective manufacturers. These can also be found as extracts in the illuminant matrix of this catalogue.
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