On Sun, 22 May 2011 00:31:29 +0000 (UTC), (Don Klipstein)
wrote:

In , Ed Pawlowski wrote:

wrote in

Sorry, but the fellow who told me that is a life-long EE, and one of the
world's leading laser experts. While watts as used in connection with
incandescent lamps has always referred to consumption, the light output
can also apparently be measured in watts. I choose to believe my friend,
whom I've known and respected for 10 years, on this score.

Absolutely. Watts-out/watts-in gives efficiency directly. W/lumen gives
a relative number but not as useful.

But what does efficiency have to do with brightness? He may be technically
correct, but how can a consumer tell what he is getting?

Say one bulb is 100 watts in, 65 watt out, it would be 65% efficient.

Another bulb is 50 watts in, 49 watts out, it would be more efficient, but
not as bright. Isn't that where the lumens comes into play? Or
candlepower?

This gets into difference between radiometric units and photometric
units.

The difference between radiometric and photometric is that photometric
takes into consideration the "photopic response" of a "standard human
eyeball", as "determned" / defined by Commission International d'Eclairage
(International Illumination Commission).

Watts radiated out by a lightbulb includes infrared and ultraviolet -
useless.

Wrong. Watts *IN* includes everything.

Watts of visible light out may or may-not include a lot of
nearly-useless wavelengths of nearly-ultraviolet or nearly-infrared.

Lumen rating is a fairly good indicator of as-seen-by-humans light
output, when determined honestly.

....and is 100% meaningless to 99.99% of the population.