On Wed, 03 Jun 2009 20:49:44 -0700, Winston
wrote:

Ned Simmons wrote:

(...)

If the filament has a thin section the power density at that spot will
indeed be higher, but the overall consumption of the lamp will be
lower. (P=V^2/R) The article says, "... we could actually see this one
patch was clearly brighter than the rest of the filament, but there
was no change in the bulb's energy usage."

Yes, but bulb life is significantly reduced.

Can we really call it a "better light bulb" if we have to replace it
~twice as often? (I don't think so.)

http://en.wikipedia.org/wiki/Incande...b#cite_note-24

"Small variations in resistivity along the filament cause "hot spots" to form
at points of higher resistivity; a variation of diameter of only 1% will cause
a 25% reduction in service life. The hot spots evaporate faster than the
rest of the filament, increasing resistance at that point—a positive feedback
which ends in the familiar tiny gap in an otherwise healthy-looking filament."

As I said above, if the experiment created a hot spot by thinning the
filament the resistance of the filament, and the power consumed, would
change. The experimenters reported there was *no change* in the power
consumption.

The relationship between power density, temperature, efficiency and
life is well understood -- you can find it in old texts that date back
to the early days of electric lighting. It's hard to believe that
these guys, whose previous work involved fiddling with the emissivity
of metals, are unaware of that relationship and have misinterpreted
the results of their experiment.

--
Ned Simmons