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How can I get Watts from Lux?

  1. Feb 17, 2016 #1
    Hello all,

    I've currently got a swirly CFL bulb that I lit up wirelessly and took some measurements of using a light sensor which returned the data to me in lux. How can I get from lux to watts? As I understand it, lux is a measurement of lumens per unit area, so do I have to somehow find the surface area of this bulb? That doesn't exactly seem simple. I've tried looking up specifications for this bulb specifically, but it doesn't include anything about surface area. The specifications available from the bulb are 2700K color and 1600 lumens. Not sure if that's entirely helpful.

    I realize you can figure out power using P = IV, but I figure that doesn't help since I only know the voltage and current input to my slayer exciter, not the voltage and current that the bulb was picking up, and I can't imagine that the slayer exciter is 100% efficient.

    Any ideas? Thanks for any help!
  2. jcsd
  3. Feb 17, 2016 #2

    Andy Resnick

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    Education Advisor

    You can convert lux to lumens by knowing the area of the detector, and convert that to Watts knowing the spectral distribution of the light (the luminous efficacy). Fluorescent bulbs and CFLs have a luminous efficacy of around 60 lm/W.

    On the other hand, since you are given the excitance (1600 lm), you can convert that to W directly (27 W), or use that information to characterize your detector, etc. etc.
  4. Feb 17, 2016 #3
    Ah, so it meant the surface area of the perceiver, not the emitter? That makes this much more simple. Thanks for your help!
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