Quantum sensor and units issue

[triscuit]

"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??

 

[vanesch]

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

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.