I didn't think there was a candlewatt but that's what the person said.
He's a helicopter pilot and said the search light on his helicopter is
30 million candlewatt.
I suspect this could be candlepower or more properly candela. Maybe it
does not achieve 30 million candela so possibly it is "rated" with some
"less scientific" form of "candlepower".
If you have a candela figure, see if you can determine the beam coverage
in steradians. (As an approximation: Determine the beam diameter in
degrees, square this figure, and divide by 4179.8. Determine the beam
width at distances far enough for this figure to not vary
significantly with distance. For a larger, narrower beam spotlight you
may need at least a few hundred meters of distance to determine the beam
width.) Divide the candela figure by the steradian figure to get (*very
approximately*!) the light output in lumens. This is only roughly, since
the beam is probably not uniform, its edges may be diffuse, the candela
figure may not be honest and some light may be found outside the beam, and
this 4179.8 "circular degrees per steradian" figure only applies for
narrow beams and then never exactly.
For comparison: A "standard" 100 watt lightbulb produces typically 1710
lumens, and the amount of "visible light" (400 to 700 nanometer range) is
approx. 6.7 watts. Also note that visible light does not always have the
same number of lumens per watt of light - the maximum is about 683, for
yellowish green monochromatic light of a wavelength of 555 nanometers.
The minimum is approaching zero, for visible wavelengths that are
borderline ultraviolet or borderline infrared.
- Don Klipstein (
[email protected])
