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Finding Spectral Illuminance from total Illuminance

  1. Feb 12, 2013 #1
    I'm trying to find the "Spectral" Illuminance (lux/nm) of a LED in order to find the spectral irradiance (watt/nm).

    I am somewhat new to optics, especially when it comes to the radiometric and photometric units.

    I understand that the Lux is just the watt/M^2 scaled to the human eye using the luminous efficacy for each wavelength.

    I want to know if this method is correct.

    What I have----
    The relative luminosity function (call it L(λ)) lm-1

    The total Illuminance from the source (~8 lux)

    What I think I need to do----

    Integrate my L(λ) function multiply by C and set that equal to 8
    C is this "normalization" constant

    (I based this off of the fact that if I have 3 lux of light A and 4 lux of light B on a surface, I will have 7 lux total. In this case A and B are different colours, and I have a full continuous spectrum of them ~350nm-600nm)

    Then the spectral Illuminance call it S(λ)
    is just C* L(λ)

    now I can take this function, C* L(λ) and divide it by the luminous efficacy function η(λ)

    finally my spectral irradiance function E(λ) is =C* L(λ) / η(λ)

    Physically this equation incorporates the LED characteristics, the measured light, and the whole lumen/watt : photo/raido metric stuff.

    Could someone tell me if this is correct and whether or not I missed something?

  2. jcsd
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