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I have an application with LED with given optical power. I found on ebay some LEDs but it appears just intensity [mcd] How can I determine optical power of LEDs in mW ?? Please, mention some clues. link with characteristics of LEDs, below : https://www.ebay.com/itm/200Pcs-3mm-5mm-LED-Light-White-Yellow-Red-Blue-Green-Assortment-Diodes-DIY-Kit/123476752059?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D1%26asc%3D20131231084308%26meid%3Da49075803d31408b809647367f4bebbd%26pid%3D100010%26rk%3D6%26rkt%3D12%26sd%3D292715528268%26itm%3D123476752059&_trksid=p2047675.c100010.m2109

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marked as duplicate by Nick Alexeev Apr 26 at 15:09

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    \$\begingroup\$ "No datasheet? No sale!" You have no idea who made those parts, what their specifications are (there is no datasheet link), what their consistency is from LED to LED, etc. If power and intensity matters to you then purchase from a supplier that sells from reliable manufacturers that publish specifications. eBay items may seem cheap but there's a reason for that. Don't buy. \$\endgroup\$ – Transistor Apr 4 at 17:33
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Optical power cannot be computed when the beam dispersion angle is unknown. Power is also a meaningless measure for an LED "indicator"

My guess is these indicators are about 10 to 20 deg.

enter image description here

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  • \$\begingroup\$ Optical power is a very important parameter when managing LED heat dissipation. The dissipated heat is total applied input minus radiated power. Some LEDs do specify the emitted power, like UV LED LTPL-C034UVHXXX, which, for example, states that for a 405-nm LED at 500 mA and typical VF of 3.7 V (1.85W) the emitted optical power is 1000 mW. Or 54% efficiency. So you only need to provide a heat sink for 850 mW dissipation. Yet the power is rarely listed, and OP's question is very important. \$\endgroup\$ – Ale..chenski Apr 4 at 18:48
  • \$\begingroup\$ @Ale..chenski These are "indicators" while your example is a high power UV "illuminator" so as long as you limit these to 20mA, the nom. current , beamwidth and Luminous Intensity [mcd] is all that counts here. ( besides color ) So Optical power is not important here at all. Do I need to define the difference between indicator and illuminator? \$\endgroup\$ – Sunnyskyguy EE75 Apr 4 at 19:01

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