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Lumens / Watts

Lumens / Watts
by shane strong on 02/14/05 at 04:19:23

Flashlight manufacturers seem to quote light output in either Lumens or Watts. I have a 3 watt output flashlight and have been offered a 5.5 lumen alternative.

How can I convert the different factors to find out which has the more powerful output

Shane Strong

Re: Lumens / Watts
by Robert Fogt on 02/16/05 at 18:00:32

You cant convert directly between them. They are measuring completly different things.

Lumens measure the flux of a light being produced by a light source or received by a surface.

Watts measure the amount of power used.

You could have a higher power flashlight, but with less light then a low power flashlight. Just depends on the light.

Unless the flashlight manufacture already has the Lumens and Watts listed, you wont be able to convert.

Re: Lumens / Watts
by Chris Ward on 12/13/05 at 14:17:17

Lumens and Watts are just photometric and radiometric terms for the same thing: optical power or flux.   The only difference is that photometry (luminous power) takes into account human perception and accounts for the sensitivity of the eye to different colors.   This can make it difficult to convert between the two unless you know the spectra of the bulb.

By definition,  at the peak sensitivity of the eye (green 555nm) 1 Watt equals 680 lumens.

It would make the most sense to talk about lumens with a flashligh, because what you really care about is the perceived "brightness", not the true optical power.


This information can be referenced on pg. 27 of "Optoelectronics", Prentice Hall 1983

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