On Tue, 02 Jun 2009 20:18:57 -0700, Winston wrote:



Sounds to me as if the modification was just redistribution of
filament metal. What would happen when you increase the resistance
of a portion of a filament by thinning it? It dissipates more power
because it's resistance is higher (P=I^2R) It glows more brightly
than the rest of the filament but will cause the bulb to fail much
earlier than it would have without the modification, I think.
Would Occam be pleased with this guess?


I got the impression that the object was to "roughen" the surface. This would
make the tungsten a better emitter. As they said, if you have good control of
the size and spacing of the asperities, you will be able to selectively change
the emissivity for different colours. If they merely wanted to selectively
thin the filament, it would be orders of magnitude cheaper to do it when
drawing the wire. Conventional bulb can (and are, for some types) be made more
efficient by using a dichroic reflector so that much of the IR gets bounced
back to the filament rather than heating the rest of the world.



Mark Rand
RTFM