Re: Here\'s a good question
My limited understanding is that Xenon molecules are large and when at high pressure, the Tungsten filament is less able to vaporise because it physically can't - The Xenon is a barrier surrounding the filament. Halogen in a incandescent bulb helps recycle Tungsten that has managed to leave the filament and deposited itself on the inside of the bulb envelope which is obviously cooler than the filament. Quite how this actually happens is a mystery to me.
The combination of Xenon and Halogen at high pressure enables filaments to be driven harder - closer to the melting point and therefore whiter.
I seem to recall this also enables funky things to be done with the thickness of the filament and the number/type of coils.
I look forward to finding out just what goes on inside an incandescent bulb!!
Al /ubbthreads/images/graemlins/grin.gif