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    georgeg
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A question on Source4 photometrics

A student of mine has asked this question from looking at the photometric data of the Source4 19 degree.

published numbers are: candelas = 243520, Field angle = 19 degrees, field lumens = 11,180

however, if you use the standard formula for calculating lumens,

F = Iv × 2π × (1 - cos(A/2))

you get F = 243520 x 2π x (1 -cos (19/2)) = 20,984 lumens.

Well, I couldn't give a good answer so I'm asking here....ANYONE??

 

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  • Hello georgeg,

    The “standard formula for computing lumens” you have must have an assumption of what the beam profile is as this equation does not seem to take that into account.  Maybe that assumption doesn’t fit the Source 4 beam profile.

    Where did you get this formula from?

    Take a look at this info on the High End site by Mikhail Dubinovskiy (How to calculate lumens output is the last point)

    http://www.highend.com/support/training/lightingfaq.asp

    Mike Meskill

     

    European Service Manager, ETC

Reply

  • Hello georgeg,

    The “standard formula for computing lumens” you have must have an assumption of what the beam profile is as this equation does not seem to take that into account.  Maybe that assumption doesn’t fit the Source 4 beam profile.

    Where did you get this formula from?

    Take a look at this info on the High End site by Mikhail Dubinovskiy (How to calculate lumens output is the last point)

    http://www.highend.com/support/training/lightingfaq.asp

    Mike Meskill

     

    European Service Manager, ETC

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