Halogen heaters.

There's actually a cycle inside the bulb where metal evaporates, turns into a halide, gets cooled on the glass envelope then migrates back to the filament.

It's called the halogen cycle.

Lightbulbs get short shrift these days but they are quite sophisticated devices.

The actual radiated heat doesn't seem all that good, I keep having the feeling that the energy converted into light would be better used if it emerged as heat instead!

It does however seem to warm the air in the room, on the coldest days the draught comes from the opposite side to which the heater is placed, the heater has a built in timer so I don't have to get up to switch it off and sitting at my desk there's a noticeable temperature drop on the windward side as soon as the heater goes off.

If you want to warm your "tootsies" as you say - it used to be possible to buy an electric blanket style foot warmer, like a giant sock for both feet at once made out of the same stuff as e/b with an element woven in. The one I have is roomy enough to keep my shoes on which is very handy - my shoes get bloody cold riding the motorcycle in this weather (freezing fog!).

Huh?

Um, guess what happens when light hits something.

Unless some of it goes out a window, virutually ALL of the light gets converted into heat.

The only exceptions would be rare photochromic reactions or whatever.

What happens is that the envelope temperature is high enough to allow a halogen/tungsten reaction, so it is 'scrubbed' of any depositing tungsten by the gas. On the filament, the temperature is so high it reverses the reaction, re-depositing the tungsten back on the filament. This leads to much longer life for a bulb operated at this temperature, making it more efficient. The bulb doesn't last forever, though, because not all the tungsten is re-deposited where it is evaporating, and eventually a weak spot fails...

Charlie

At first I was worried about where to site the heater in case the radiated heat scorched nearby furniture - but there doesn't seem to be that much radiated heat, at least none of the furniture illuminated by the heater gets any more than barely warm.

Seems there's physics and then there's what actually happens in real life!

I have a cooking stove with halogen heaters. It adjusts the temperature by varying the duty cycle at a very slow rate. LOW might be 2 seconds ON every

Tam

Sounds like they use the same old "simmerstat" switches as the bog standard electric hob rings, this is nothing more than an adjustable bi-metal strip with a coil of resistance wire wound round it.

The halogen cycle DEMANDS cooling periods, or the process will not work.

Does that apply only to cooker hobs? The halogen heater I have has a 7-1/2 hour timer.

Thanks for the info. That explains why even on HIGH it does not stay on continuously; turns off briefly every 5 - 10 seconds.

Tam