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128 General Information
TECHNICAL
Luminous Efficacy
Unit of measurement: lumen per watt
[lm/W]: Luminous efficacy indicates
the efficiency with which the electrical
power consumed is converted into
light.
The maximum that can be achieved
in theory, with all the energy being
converted into visible light, is 683
lm/W. In reality, the figures are much
lower, between 10 and 150 lm/W.
Luminous efficacies of
various light sources
1000
100
10
683 lm/W = Theoretical limit for
monochrome green light (555nm)
199lm/W = Theoretical limit for
"white" light (380–780nm)
Low Pressure Sodium Lamps
High Pressure Sodium Lamps
Fluorescent, Metal Halide, Yellow Compact,
Xenarc Lamps
High Pressure Mercury Vapour Lamps
High Intensity white LED
Special Light Bulbs Xenon Lamps,
Mercury Tungsten Blended Lamps
Tungsten-Halogen Lamps
General Lighting Service Lamps
Colour Rendering
Depending on the location and the
purpose, artificial light should enable
colours to be perceived correctly, as
though being seen by natural daylight.
Such assessments are based on the
colour rendering properties of a light
source, which are expressed in terms
of categories of the general colour
rendering index, R a. The colour
rendering index is a measure of the
correspondence between the colour
of an object under the light source
being measured and its colour under a
reference light source.
Carbon Thread Incandescent Lamps
1
Glow Lamps, Electroluminiscent Plate
Paraffin Lamp
lm/W
0.1
Candle
Incandescent and Halogen
Lamp Operation
Incandescent lamps are classic thermal
radiators in which electricity flows through
a Tungsten wire in an enclosed glass bulb
filled with a vacuum or inert gas, heating
it to approximately 2600˚C to 3000˚C and
making it glow. Most of the radiation emitted
is at the infra-red end of the spectrum.
L e λ ref
Luminous efficacies of various light sources
4
3
2
1
UV - radiation
IR radiation
Tw 2800˚C
Tw 2600˚C
Tungsten filament winding
temperatures T w
for incandescent lamps
2400˚C corresponds to a
15W lamp (vacuum bulb)
2600˚C corresponds to a
40W lamp (bulb filled with gas)
2800˚C corresponds to a
500W lamp (bulb filled with gas)
Tw 2400˚C
0
1000
2000 3000 4000
5000
visible light
wave length unit of measure nm
Relative Spectral Power Distribution Of Incandescent Lamps
The main properties of an incandescent lamp, namely its luminous efficacy and
life, are influenced largely by the filament temperature.