In , Lostgallifreyan wrote:
(Don Klipstein) wrote in
:

The steepness of that curve alone is enough to make large changes in
output of visible lumens with small changes in voltage.

Yes, quite true. But at full voltage most 120V incandescents 60
watts
or more are about 4.5-8% efficient at converting electricity to
radiation in the 400-700 nm range.

Is this by calculation or measurement? I was hoping you or someone else
would comment on that from experience with it. Those lower figures are so
common that they must have come from somewhere, and not all from looking
only at the strongest wavelength or omitting something in calculation. I've
never seen claims of 6 to 7% for a 100W lightbulb before, and I'm sure I
would if measurements routinely reported it.

They do lots of photometric measurements, while radiometric figures for
incandescents appear to me to be rather rare. More common than actual
measurements I see comments in the direction of "close enough to
blackbody".

http://www.uwsp.edu/cnr/WCEE/keep/Mo...Conversion.htm
says most incandescents are about 5% efficienct

http://www.iiasa.ac.at/Publications/.../IR-04-027.pdf
also gives a 5% figure

Osram says 5% he
http://catalog.osram-os.com/catalogu...do;jsessionid=
337BCEEB510F317E25E607F73C895CFB?act=downloadFile& favOid=
020000020003caf0000100b6

http://www.healthyhomemagazine.ca/light.html
says 4-6%, attributed to someone at Natural Resources Canada.

http://www.eia.doe.gov/kids/energyfa...ingenergy.html
says 10%

http://oikos.com/esb/40/kitlight.html says 10%

10% I find to be a somewhat common figure, though rather optimistic.
Some of those 10% figures may be based on an alternative definition of
visible light as 380-760 nm rather than 400-700 nm.

- Don Klipstein )