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Author Topic: Microwaved light bulbs  (Read 10907 times)

paul.fr

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Microwaved light bulbs
« on: 27/03/2007 09:40:14 »
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


 

Offline daveshorts

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Microwaved light bulbs
« Reply #1 on: 27/03/2007 09:54:26 »
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

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Microwaved light bulbs
« Reply #2 on: 27/03/2007 09:57:29 »
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?
« Last Edit: 27/03/2007 10:13:36 by paul.fr »
 

Offline daveshorts

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Microwaved light bulbs
« Reply #3 on: 27/03/2007 11:04:35 »
I think mercury gives a bluey white colour with a lot of UV in the light given off.
 

Offline lightarrow

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Microwaved light bulbs
« Reply #4 on: 27/03/2007 14:56:58 »
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.
« Last Edit: 27/03/2007 15:00:55 by lightarrow »
 

Offline daveshorts

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Microwaved light bulbs
« Reply #5 on: 27/03/2007 15:29:39 »
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.
 

Offline Karen W.

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« Reply #6 on: 27/03/2007 17:42:17 »
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?
« Last Edit: 28/03/2007 02:28:21 by Karen W. »
 

Offline daveshorts

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Microwaved light bulbs
« Reply #7 on: 27/03/2007 20:20:11 »
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.
 

Offline Bored chemist

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« Reply #8 on: 27/03/2007 20:33:58 »
"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

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Microwaved light bulbs
« Reply #9 on: 27/03/2007 20:50:24 »
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

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Microwaved light bulbs
« Reply #10 on: 27/03/2007 20:53:02 »
"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.
 

Offline Karen W.

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« Reply #11 on: 28/03/2007 02:30:19 »
Thanks guys!!
 

Offline daveshorts

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Microwaved light bulbs
« Reply #12 on: 28/03/2007 10:06:18 »
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

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Microwaved light bulbs
« Reply #13 on: 28/03/2007 10:11:42 »
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!
 

Offline Karen W.

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« Reply #14 on: 28/03/2007 16:40:50 »
Isn't Mercury extremely poison and in what way?
 

Offline daveshorts

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Microwaved light bulbs
« Reply #15 on: 29/03/2007 07:23:36 »
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'
 

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« Reply #16 on: 29/03/2007 09:52:48 »
Do they still use mercury in themometers?
 

Offline Bored chemist

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« Reply #17 on: 29/03/2007 20:03:55 »
Yes.
 

Offline Karen W.

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« Reply #18 on: 30/03/2007 06:31:05 »
What do they put mercury in the bulb for Paul or Dave or who ever knows?
 

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Microwaved light bulbs
« Reply #19 on: 30/03/2007 09:43:58 »
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.
 

paul.fr

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Microwaved light bulbs
« Reply #20 on: 30/03/2007 09:54:41 »
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.

Dave, is phosphor the white powdery substance in the flourescent tube? If so what actions should one take, if any, if the tube smashes and you get some of the phosphur on yourself or inhale it?
 

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« Reply #21 on: 03/04/2007 10:31:01 »
I do believe it is! But not positive
 

Offline eric l

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Microwaved light bulbs
« Reply #22 on: 03/04/2007 17:22:10 »
Actually, the powder is not phosphor(us), but a mixture of phosphorous salts.  (see also :  http://en.wikipedia.org/wiki/Fluorescent_tube)  This means that they are not classified as "dangerous substances" to the same degree as the "metalic" phosphorus.  Still, it is not advisable to inhale them or anything like that (but they will not create a fire when exposed to air).
 

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Microwaved light bulbs
« Reply #23 on: 03/04/2007 18:54:41 »
A phosphor and phosphorous are two different things.

 A phosphor is something which when given energy, by UV or high energy electrons will give off light, zinc sulphide is the tradidional one, but I am sure they use more exotic things in a fluorescent tube.

 Phosphorous is an element that is very flamable, and some allotropes will glow if exposed to oxygen. Some types will catch fire just by exposing them to oxygen. It burns very brightly and is often used for flares and illumination grenades.
 

Offline Bored chemist

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« Reply #24 on: 03/04/2007 19:50:00 »
Long ago they used beryllium silicates in the phosphors in fluorescent tubes. Since Beryllium compounds are pretty toxic, various scare stories grew up about the stuff in the tubes (notably a myth that the stuff was radioactive). It's probably not a good idea to inhale or ingest these phosphors but the newer ones are less toxic- at least to the extent that you should worry about the mercury instead.
(BTW, IIRC metalic phosphorus is one of the least nasty forms)
 

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Microwaved light bulbs
« Reply #24 on: 03/04/2007 19:50:00 »

 

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