Lighting Design and Simulation Knowledgebase
(Term of photometry)
Luminous flux is photometrically weighted radiant flux (power).
At a frequency of 540 x 1012 Hertz, it is defined as 683 lm/W of radiant flux. As with luminous intensity, the luminous flux of light with other wavelengths can be calculated using the CIE photometric curve.
The luminous flux is a very basic unit of measurement for light.
If a uniform point light source of 1 cd luminous intensity
(about the intensity of a normal wax candle!) is positioned
at the center of a sphere of 1 m radius, then every area
of 1 m2 on the inside of that sphere will
receive a luminous flux of 1 lm.
(This relation also holds when using other units
like 1 ft radius and 1 ft2 area.)
Since the surface area of a full sphere is 4*Pi times the
square of the radius, a uniform point light source of
1 cd produces a total 12.57 lm of luminous flux.
Most real life light sources area not uniform though.
This factor is therefore only useful for rough estimations
and will normally give inaccurate results.
Standard unit of luminous flux is Lumen (lm).
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References: |
luminous intensity photometry radiant flux wavelength |
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| English | German | |
| luminous flux | Der Lichtstrom |
