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Quantum sensor and units issue

  1. Jan 31, 2008 #1
    "quantum sensor" and units issue

    I'm working on an wireless sensor network for a commercial greenhouse concerned with energy use and efficiency. Much of the literature regarding photosynthetic active radiation uses watts/square meter, but the client has requested a measurement in micromoles/square meter/second as the photon flux density. The commercially available "quantum sensors" use this unit, but we would like to use an array of simple photodiodes as a cost effective alternative.

    So, how do you convert from W/m2 to umol/m2/s? We will specifically be looking at and distinguishing between wavelengths 400-500 and 600-700 (because that's what the plants need). If we use a passive sensor with a voltage output, how do I translate that into moles of photons??
  2. jcsd
  3. Jan 31, 2008 #2


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    haha, that's funny, I never heard the expression "a mole of photons" before :smile:

    Now, the conversion is very simple:

    if v is the frequency of the light (in Hz), then the energy of a mole of photons is given by:

    E = h x Na x v

    where h is Planck's constant and Na is Avogadro's constant.

    A mole of photons per second is then the above expression in Watts.
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