# Calculating radiant power of LED over its whole spectrum

1. Nov 3, 2012

### picobyte88

Hello

OK so I'm very new to electronics and I really need some clarification/guidance. I am using this integrating sphere which is basically just a glorified photodiode.

I am going to be measuring the output photocurrent using the responsivity curve of the photodiode. The sphere also has a port for measuring the spectrum of the light source which in this case is an LED. Using a simple multimeter I can measure the photocurrent which lets say for example is 10uA.

I can simultaneously measure the spectrum of the LED using a spectrometer from which I get the intensity in arbitrary units as a function of wavelength. Now I have the responsivity curve i.e. the responsivity as a function of wavelength of the photodiode detector but what I want to do is calculate the total radiant power over the whole spectrum of the LED.

So do I find the power for each wavelength using the responsivity of the photodiode? so for example with a photocurrent of 10uA at a wavelength of 500nm which corresponds to responsivity of 0.6A/W I get 0.016mW radiant power

So do I then at 505nm which corresponds to responsivity of 0.58A/W calculate 10u/0.58 = 0.017mW? i.e. can I use the same photocurrent when calculating the radiant power at each wavelength as long as I use the corresponding responsivity? and then can I just sum up all the powers at each wavelength to get the total radiant power over the whole spectrum of the LED?

But do I also need to take into account the intensity vs wavelength spectrum measured as well?

I'm so confused!!!