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Units and Formulas
1. Variables and units in lighting technology
LUMINOUS FLUX
Φ
ILLUMINANCE E
LUMINOUS INTENSITY I
Variable
Symbol Unit
De nition
Luminous
ux
Φ
Lumen (Im)
The light of a light source
Luminous intensity of a light emitting surface
divided by the size of the perceived surface or:
the brightness of a diuse re ecting surface,
determined by multiplying illuminance with
re ectance divided by p
Luminous ux incident on a surface area
divided by the size of the surface area
Intensity of the light output in a specic
direction (luminous ux/solid angle)
Luminous
intensity
I
Candela (cd)
Illuminance
E Lux (Ix)
Luminance
L
cd/m
2
cd/cm
2
Variable
Symbol
Ratio
De nition
Luminous ecacy
of a light source
Emitted luminous ux on the utilized area divided by the total ux of all
the lamps in a lighting installation
Ratio of a lighting installations’ luminous ux on the utilized area to the
total ux emitted to the room by the luminaires
Ratio of the total ux of the luminaire, measured under specic
practical conditions, to the sum of the individual luminous uxes of the
lamps operating outside the luminaire under specic conditions
Emitted luminous ux divided by the power input of the lamps
η
η
=
Φ
Lp
P
Light output ratio
η
LB
η
LB =
Φ
L (tL )
ΣΦ
Lp
Utilance
η
R
η
R =
Φ
N
ΣΦ
L
Utilization factor
η
B
η
B =
Φ
N
ΣΦ
Lp
η
B =
η
R
•
η
LB
2. Operating ratios in lighting technology
Appendix>
Lighting Technology
Philips Lamps and Lighting Electronic Catalogue 2014
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