Luminous Intensity
Candlepower (USA)
(Term of photometry)
The luminous intensity is the luminous flux
emitted from a point per unit solid angle
into a particular direction.
The luminous intensity is the official base unit for light.
It was defined in 1996 by the
"Conférence Générale des Poids et Mesures"
(CGPM, the 11th General Conference on Weights and Measures)
as follows:
The candela is the luminous intensity, in a given direction,
of a source that emits monochromatic radiation of frequency
540 x 1012 hertz and that has a radiant
intensity in that direction of 1/683 watt per steradian.
Together with the CIE photometric curve, the luminous
intensity provides the weighting factor needed to
convert between radiometric and photometric measurements.
Standard unit of luminous intensity is Candela (cd),
also expressed as Lumen per Steradian (lm/sr)
There are several older units of luminous intensity:
|
Candle (deprecated)
|
1 candle = 1.02 cd
|
Hefner unit (deprecated)
Hefner candle (deprecated)
|
1 hefner unit = 0.9 candle
|
|
Violle (deprecated)
|
1 violle = 20.17 cd
(1 violle is the luminous intensity of
1 cm2 of
platinum at its temperature of solidification
of 1042 kelvin)
|
| 
