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## Power Input Question

• 8/11/2021
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I'm designing a color mixed light source and trying to achieve a dense array of Rebel LEDs, which leads to the expected thermal management issues.  In the application notes you list the power input to the thermal resistance equations as (forward voltage * forward current).  Is all of that power converted to heat?

Looking at the Royal Blue parts, I*V is 0.7A * 3.4V = 2.38W, but the data sheet lists the light output as 0.74W.  Is it then safe to assume that the heat output is 2.38 - 0.74 = 1.64W?

If so, how is the light energy output calculated for the parts specified in lumens?

Replies
• 8/12/2021

You calculations are correct. As for the LEDs that have the flux in lumens, the photometric flux can be converted to radiometric flux using the wavelength of the LED and its lumen output, using a luminous efficiency factor (which is wavelength dependant) There are tables available that have that factor for each wavelength and you can use it to convert from one flux to the other.