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How do I measure the optical power output of a LED? I have a detector that measures the output power of a laser incident on a small opening. The problem with using the LED with the same detector is that its light is dispersed and I don't have a model that quantifies the distribution of the LED light in space, with which I can calculate the total power based on information of power incident on the small opening.

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  • $\begingroup$ Google "integrating sphere". $\endgroup$ – The Photon Feb 20 '17 at 23:42
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    $\begingroup$ converging lens? $\endgroup$ – M. Enns Feb 20 '17 at 23:50
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  1. If you want to measure the total power of a LED in Lab, you can place it in a focal point of a concave mirror and after collimating beam focus it to your detector with a lens:

enter image description here

note that the loss for an uncoated lens is about 9% of total power and mirror loss is negligible.

  1. simpler way is, of course, find the part number of the LED and see the catalog. because solid state diode emits light in term of a sophisticated function and it is not simple to find the angular distribution with a number of measurements.
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If your LED has decent power and your power meter is sensitive and if you know the area of the aperture you could make an estimate but it might take a few measurements at different angles. A LED's light distribution is called Lambertian and the formula is available online. You would need to assume your power meter is calibrated and that it performs well over its known area surface.

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