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Thread: A question of intensity...

  1. #1
    Join Date
    Feb 2009
    Brighton, East sussex, UK

    Lightbulb A question of intensity...

    Hello to all the gentlefolk on PL,

    I have what may seem like a silly question, Is it possible to convert the perceived intensity of a relatively monochromatic light source 'lumens' (i'm assuming photopic vision) in to a radiometric intensity milliwatts? Assuming that you know the wavelength and the average eyes response curve.

    If so could somebody provide me with a formula to do this as even after an extensive searching, Google/my brain appears to have failed me!!!

    Any help would be greatly appreciated

    The mind is like a parachute, It doesn't work if it's not open...

  2. #2
    Join Date
    Aug 2008


    Its possible to do it the other way around using Chroma ie to turn Milliwatts into lumens.

    However, I'm not sure this helps you with what I think you're trying to get at as beam brightness is related not only to brightness but the density ie the area over which the beam is concentrated.

    eg A modern HID torch may produce 3,000 lumens and a watt of 532nm laser only 600, but the big difference is that torch beam is spread out over a large area with light spreading randomly in all directions whereas with a laser its all travelling in the same direction in a concentrated beam a few mm across.

    I'm also guessing that when it comes to measuring lumens from lasers, the luminosity reading is taken from the side and thus represents general radiated brightness, (I stand to be corrected on that), and not from head on as given that a 1mw pointer is according to a source I googled 167 times brighter than the sun which in turn is a ridiulous amount of lumens in brightness - according to the Net Wiki 3.84610 to the power of 26
    in Watts!!!

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