If I spray a light bulb matt black so no light can escape, does this cause all the energy it dissipates to be converted into 100% heat instead of just heat+light and would this cause the bulb to run hotter as a result?
cheers.
yes.
ISTR that virtually all the energy released is heat anyway, the actual amount of energy contained in the visible light is miniscule.
I think it would run hotter since the paint would absorb infra-red that would otherwise be radiated and the paint would act as an insulator.
the energy it dissipates to be converted into 100% heat instead of just heat+light
and would this cause the bulb to run hotter as a result?
If you paint a bulb red with artists oil paint it smalls badly when it gets hot.
Bill
If you paint it with liquid bullshit it turns to solid bullshit when it gets hot
Obviously since then visible light would no longer escape and so the thermal and IR radiation component would have to increase to compensate so it must get hotter to dissipate roughly the same amount of power. It would emit radiation characteristics of a black body with the surface temperature of the outer glass envelope instead of the filament inside.
But it would be even hotter still if you surface coated the bulb with a high mirror finish - since a mirror surface is a very poor emitter of electromagnetic radiation. Aluminium spray would do at a pinch.
Selective IR only mirrors are used on sodium street lamps to improve their thermodynamic efficiency - preventing an IR line from escaping and making it easier for the tube to warm up to operating temperature.
It would be impossible for it to suck in any dark.
On Thursday 01 August 2013 23:28 snipped-for-privacy@virgin.net wrote in uk.d-i-y:
Yes and yes.
Yes.
I did this when young, in one case it actually broke after only a few minutes. Mostly it ponged a great deal though. Brian
I think it would just run hotter, the light is still being produced. Unless this is a home made black hole, which is something light[1] doesnt escape from ;-)
[1] well Harwkins radaition does, but I don;t see that as light
It's the paint that smells I did that with normal paint when I wanted a cheap darkroom safe light it was one of those 15W pigmy bulbs.
Sorry, not really. Even with very dense paints the filament would suck the dark. Unfortunately there can be so much dark in a decent quality black paint coating that the filament gets "overloaded" and often suffers a premature death before all the dark in the paint is adsorbed.
For anyone with a few dozen planet destroying 100W darksuckers and a bit of scientific curiosity it can be shown that the filaments indeed wear out before the paint loses its dark.
AB
Not sure why everyone seems to be assuming it's a tungsten lamp; it isn't. It's one of these energy efficient jobbies in the 'golf ball' shape. Neithe r is the idea to make the bulb run hotter internally; it's to try to get it to radiate a bit more heat into its environment in order to keep condensat ion away from the device mounted directly above it. Hope that clarifies thi ngs a bit. Actually, at a rated 5W, it's doing pretty well as it is, but a marginal increase in heat output would still be welcome.
Not normally, but on a black hole small enough to be emitting at a reasonable rate it would be. A black hole just looks like a cold black body, until it's small when it gets hot. Probably very hot, very quickly.
Andy
It has to be pretty small to radiate significant amounts, atom-sized IIRC.
These devices are very poor "darksuckers" there isn't a filament if I remember correctly. Personally I would stick a thermometer on the thing you are heating and then apply various waterpaints to your darksucker. I think it's safe to generalise that a greater temperature = less condensation. I would doubt very much if there were a noteable change though.
The advantage of waterpaints is that they can be removed easily. The fact that your particular darksucker is so wimpish has the dubious advantage that it will not have the ability to engorge itself to destruction, thus living on to suck a little more dark for years to come.
AB
t. It's one of these energy efficient jobbies in the 'golf ball' shape. Nei ther is the idea to make the bulb run hotter internally; it's to try to get it to radiate a bit more heat into its environment in order to keep conden sation away from the device mounted directly above it. Hope that clarifies things a bit. Actually, at a rated 5W, it's doing pretty well as it is, but a marginal increase in heat output would still be welcome.
Yeah, point taken. I initially would have gone with 20W-25W but so many peo ple told me it was way too much and they were right. 5W seems to be just ab out perfect for this application. 25W would have melted the device it was s upposed to protect, I reckon! ;)
It all ends up as heat anyway. The bit of light will become heat as soon as its absorbed by the environment.
Try not warming the base much as it will wreck the electronics, they like to be cool at all times. Probably why most people would use a tungsten lamp or better two in series.
Because that is the most obvious choice of lamp. Cheap and cheerful.
You are dumber than a rock. Energy efficient lamps are more efficient at producing *light* - covering them in black paint is very stupid. Low efficiency tungsten lights already waste most of their input power as heat and are an order of magnitude cheaper to buy.
That is the principal effect that it will have and it will shorten the lifetime of the lamp control electronics. You have an expensive device to shorten the lifetime of a CFL bulb. Well done!
If you want to do that buy a warm air thermostatic radiator device intended to do the job of producing a flow of warm air!
A pair of 15W incandescent lights in series would be your best bet then for DIY. Or perhaps even better something actually designed to actually do this sort of job safely in an exterior building like a greenhouse:
Cheap perhaps, but not very cheerful.
I've specifically avoided tungsten lamps because they don't last 5 minutes nowadays. I need to be able to leave this on for months on end without fretting that it will have got "phut" whilst I'm away for any extended period!
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