# Calculate optical power output of LEDs

1. Oct 24, 2013

### Sophie MC

Hi guys,

I have to calculate de optical power output of a set of LEDs. For that I used a photodiode to measure the photocurrent at each wavelength and then calculate the optical power at each wavelength using the following formula:

R (A/W) = I/P,

where R is the responsivity of the photodiode at each wavelength,
I is the photocurrent measure with the photodiode at each wavelength and
P is the optical power output at each wavelength that I want to measure.

I have de responsivity curve of my photodiode and I have measure the photocurrent. However when calculating de optical power output I obtain very small values.

For example, for a LED with typical 17000 mlm (from datasheet), I only obtain 0,027 mW (summation of all wavelegths) of optical power. I think that this is a very small value comparing with the value in lumens (17000 mlm).

Can any on help with this? Am I right? Am I wrong? Is this the right way of calculate optical power?

Thank you so much