[paul.fr]

is was going to do this and post it in the "what's your kitchen science" topic, but for reasons of safety i will not. I would still like an answer as to the why of the experiment though.

I was trying different light bulbs in the microwave, the first one i tried was a opaque 40watt bulb and i put it in for 4 seconds. it gave off a lovely orange colour!

secondly i tried a standard 60 watt bulb, in the same 4 seconds it gave off first orange, then red and yellow light...then blew up.

i never got to try the third bulb.

why does the light bulb give off different colours when heated in a microwave?


For safety reasons i would not reccomend doing this at home

[daveshorts]

Orange, then red, then yellow sounds like it is something getting hotter, possibly just the filament. You can also get purples which is essentially sparks travelling through the argon the bulbs are fillled with. You can occasionally get a green colour which I think is the tungsten of the filament evaporating and the spark going through it.

[paul.fr]

cheers dave, i did get purple that was the initial colour! but forgot that. my third bulb was a halogen containing mercury, i did not want to try that one after the spectacular mess the second one made.

what could i have expected from that type of bulb?

[daveshorts]

I think mercury gives a bluey white colour with a lot of UV in the light given off.

[lightarrow]

Orange, then red, then yellow sounds like it is something getting hotter, possibly just the filament.

Orange then red and then yellow sounds quite strange for something getting hotter; I would expect red then orange and then yellow, instead.

Maybe the filament became orange at first, then it heated more, together with some other part of the lamp and the yellow came from the filament and the red from this other part.

[daveshorts]

Ooops yes you are right. What normally happens is that the filament burns out first with a flash of light (you are putting a kilowatt into a 60W bulb) then the other metal bits heat up and start to glow, with random purple and green sparks thrown in - these are basically making light like a neon tub rather than just a hot thing.

[Karen W.]

I would never of thought to nook a light bulb.. What are the lights inside of the microwaves made from, and why does the microwaving not effect their own bulbs Paul?

[daveshorts]

They put the light bulbs behind a metal grill which keeps most of the microwaves away from the bulb, in the same way as the grill in the door keeps them away from you.

[Bored chemist]

"my third bulb was a halogen containing mercury,"
Who puts mercury in halogen lamps? Is it a mercury/ metal halide lamp or a tungsten lamp or an tungsten halogen lamp?

[paul.fr]

I would never of thought to nook a light bulb.. What are the lights inside if the micrawaves, and why does the micrawaving not effect their own bulbs Paul?

what dave said. it's one of those i always meant to do but never got around to until now.

[paul.fr]

"my third bulb was a halogen containing mercury,"
Who puts mercury in halogen lamps? Is it a mercury/ metal halide lamp or a tungsten lamp or an tungsten halogen lamp?

My apologies to you BC and anyone else who were confused. I was very tired and just read the post about halogen bulbs and put halogen.

the third bulb was actually a fluorescent bulb which contained mercury...my sleep deprived confusion. sorry again.

[Karen W.]

Thanks guys!!

[daveshorts]

fluorescent tubes just light up in the microwave, although don't cook them for more than 4-5 seconds as it is entirely possible to melt bulbs in there, and releasing the mercury would be bad.

I don't know what a compact fluorescent would do (the low energy light bulbs), it would probably light up, but I think the circuitry in there would probably melt, and make lots of nasty smells..

[paul.fr]

fluorescent tubes just light up in the microwave, although don't cook them for more than 4-5 seconds as it is entirely possible to melt bulbs in there, and releasing the mercury would be bad.

cheers, Dave. The realease of mercury was the main reason i never tried the third bulb as i did not know the time frame from just a glow, to bang!

[Karen W.]

Isn't Mercury extremely poison and in what way?

[daveshorts]

It does bad things to your brain - mercury compounds were used in making felt for hats, which is the reason for the phrase 'mad as a hatter'

[Karen W.]

Do they still use mercury in themometers?

[Bored chemist]

Yes.

[Karen W.]

What do they put mercury in the bulb for Paul or Dave or who ever knows?

[daveshorts]

Fluorescent bulbs work by giving a gas lots of energy electrically which they then emit as light. The difficult thing is to find a gas that emits light at the right frequencies. For example sodium vapour makes an orange colour (eg streetlights) neon gas makes a red colour. I think there is a mixture of gasses in a flourescent tube one of which is mercury which emits in the visible range and in UV - the UV is then converted into visible light using a phosphor. I guess mercury is the best mixture of colour and efficiency available.