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How many lumens is 30 million candlewatts?

Discussion in 'Lighting' started by Michael Shaffer, Mar 6, 2004.

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  1. Title says it all
  2. 42.
  3. My previous answer ("42") was an approximation assuming proper
    measurement. If you are looking for an exact measure, we need more
    information. How was the 30,000,000 candlewatts measured? You really need
    to use a fimble damper and a mass-transit (NOT a weight-transit!) to get
    an accurate reading, otherwise the Kempfthorne Effect tends to grossly
    distort your readings and you'll get a garbage answer.

    What's the nature of your project, that you're measuring in candlewatts
    rather than the more commonly used Amplumens or Ouncelamberts?

  4. Candlewatts are not a unit of anything. Do you perhaps mean
    candlepower? But then again, even candlepower is not a unit of light
    but rather the luminous intensity of a light source in a given
    direction, where the units are usually given in candelas.

    If, and only if, your light source had a mean spherical candlepower of
    30 million candela, then it would produce 4 PI times 30 million or 377
    million lumens. If you do not know the mean spherical candlepower,
    then you would need the candlepower distribution in each individual
    direction in order to compute the output in lumens.
  5. 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.
  6. I asked him the lumens and he told me candlewatts.. I guess I was just
    wondering how much light it puts out compared to a normal 100w bulb for
  7. 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 ()
  8. Thank you, Deep Thought

    Jeff Waymouth
  9. Short arc xenon lamps of wattage near this have a luminous efficacy
    around 40 lumens per watt. This means a 1300 W one would produce
    somewhere around 52,000 lumens. 1600 watt ones produce 60,000 lumens.
    Not all of this will be formed into a beam by the reflector.

    - Don Klipstein ()
  10. R.Lewis

    R.Lewis Guest

    Only those used on 1960-1970 Ford Populars.
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