# Detecting how bright is the sun using a photodiode [closed]

Basically I'm trying to control the moment when I turn on the lights using a photodiode. Let's say when the sun illuminance is 10lx, the photodiode will read a given value in $$\frac{W}{cm^2}$$. Given the luminosity function $$v(\lambda)$$ the photodiode sensitivity (mainly infrared) curve and the sun spectrum is there a way to find this correlation? I tried to integrate $$v(\lambda)$$ multiplied by the sun spectrum and the same for the photodiode sensitivity and found a ratio which does not fit to my measurements.

## closed as off-topic by Aaron Stevens, The Photon, Jon Custer, GiorgioP, M. EnnsJun 13 at 18:56

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• I did not understand what you meant by Luminosity function. Did you quantity them or have a proper numerical expression for each of them? – lattitude Jun 11 at 14:33
• Sorry, the luminosity function is related to the human eye sensitivity. These values are tabulated and provided by the CIE. – Hagah Jun 11 at 14:34
• Here your detector will use light directly from the sun. You don't use you eyes to do anything in your device right? Then, there is no link to what you eye sees and therefore luminosity function has nothing to do with this calculation – lattitude Jun 11 at 14:39
• @latitude, the luminosity function is related to when we'd want to turn on the lights to make it easier to see things around us. – The Photon Jun 11 at 15:07
• @Hagan, you can buy a photodiode that's calibrated relative to luminosity rather than radiative flux. Or you can make the turn-on threshold adjustable, and adjust it based on your own perception of brightness. But this is more of an engineering question than physics. – The Photon Jun 11 at 15:10