Vapourised Tungsten

About 3 years ago when I put this bulb in to the oven to replace it's defunct predecessor. Back then, it was clear glass with a neatly coiled tungsten filament. The other day I was sitting reading in the kitchen while lunch was cooking, and suddenly there was a bright flash from the oven and it went dead. I thought I was going to be eating cold lunch, but fortunately it came back on once I reset the circuit breaker - albeit without the light working.

We never really consider the lives of lightbulbs, but as they are being slowly replaced by the ghastly green flickery light of CFLs (which when you factor in manufacturing impact aren't even that good for the environment, unless you use air conditioning in the same location) I thought I would mark the passing of this particular bulb with a reflection of its life - a commonplace story, but remarkable nontheless.

Since the day that it was installed, every second it has been turned on, atoms of tungsten have been evaporating from its filament. Remarkable - metal atoms literally boiling. It's probably happening all over your house - right now!

Have you ever tried to change a light bulb without leaving it turned off for a while first? If so you'll know the glass gets pretty hot. Very hot in fact - burningly so. The thing is, that to these boiled tungsten atoms, the glass is cool, so they condense there. Just like steam on a mirror. As the bulb gets older, the glass becomes more and more mirror-like as a layer of tungsten accumulates on the inner surface.

Eventually, too much tungsten evaporates from the filament, and the power is just too much for the little that is left. At this point, a tiny weak spot will form and at that point heat will accumulate... Until in a final flash of glory the filament burns out in a small explosion of molten metal.

All that remains now is a dead bulb...

Boiling metal, condensation on glass hot enough to boil water, and a final explosion. Incandescant light bulbs have much more interesting lives than you might imagine.


I'll retreat to my geek corner now