How to convert photodiode voltage to any photonic unit

[rc101268]

How can I convert the voltge measured across a photodiode to light output or intensity or any other photonic unit?
I am trying to measure the light intensity/output of some LEDs using a photodiode but the photodiode measures voltage as a function of light intensity.

 

[mrspeedybob]

I would try to calibrate it using a light source of known intensity. Some light bulbs have their light output printed on the package. Look for lumens, not watts. You'll have to find out the distance from the bulb that the intensity is measured but once you have that you can set up your detector at that distance in an otherwise dark room and measure voltage. Then you'll know that X lumens results in Y volts. With several X and Y data points you should be able to make a good graph to correlate voltage to lumens.

 

[rc101268]

^^
Thanks
The radiant power(watt) of the LED plotted against time is given in percentage on the data sheet, but no information on the distance it was measured.
I want to believe this radiant power is equal to the lighting flux?

 

[fidy999]

I believe that radiant flux and luminous flux (lux) are two different quantifications- one measures intensity of light based on power (watts) the latter measures light intensity in terms of perceived reactivity in the human eye.

Tell me if I am right or wrong about that.

Also, I had a question that is along the lines of this thread: if i had a light intensity meter (lux or radiant flux) and I went outside in the sun and pointed it straight at the sun, then to 45 degrees from direct incidence, and then 90 degrees, 180 degrees... I would expect to see changes in Watts right?

If yes, now let's assume I have a PV panel that is some angle delta theta away from direct sunlight incidence, would the output power of my PV panel be therefore less?
At 45, 90, 180 degrees?