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Don Klipstein

In , zzzzz wrote:
On 21 May 2011 13:47:01 -0400, "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?

Visible energy out is the whole point of a light bulb, isn't it?

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

Ok...

Another bulb is 50 watts in, 49 watts out, it would be more efficient, but
not as bright.

Do you want a 49 watt out bulb or a 65 watt out bulb? If you only need 49W of
illumination, certainly you would buy the smaller bulb.

Isn't that where the lumens comes into play? Or candlepower?

Yes, but power is power (A candela is 4*pi*lumens ;-).

A candela is 4*pi lumens for a uniformly even omnidirectional light
source. A "MSCP" or "mean spherical candlepower" is 4*pi lumens.

A candela of anything more directional than "100% in all directions
in all combinations of both ways of all 3 dimensions" is a different
number of lumens, generally less since candela gets measured where the
light goes.

Light sources that have greater directivity, greater concentration of
their light into a specific direction, have higher ratio of
candelas/lumens. The risk or downside from that is illumination being
concentrated to an area smaller than what you want illuminated, or
shortage of background illumination or overall "ambient illumination".

There are many people who don't work at 100% if illumination is
restricted to some "task area".
--
- Don Klipstein )