# Halogen bulb, wattage rating, heat output

Discussion in 'Highly Technical' started by RU482, Dec 12, 2003.

1. ### RU482 Lifer

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I half assedly made a comment in a thread about cheap halgen work lights about using them as a dual purpose device (light and heat). I went on to ask how many BTU's a 500W halogen lamp would put out.

Now, I would think that some of the 500W goes towards creating light. How much of it is lost to heat?

I know that .5 kw-h = ~1700 BTU
I was considering buying a 1 kw space heater.
How close would 2 500W halogen lamps come to a 1000W space heater?
Additionally, I could fabricate a metal bracket to hold a, say, case fan that would blow air across the surface of the light to spread the conducted heat. Sounds like an intersting experiment and a way to utilize the thermocouples on my multimeter

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3. ### CTho9305 Elite Member

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All of it goes to heat. Whether it is directly converted at the bulb, or at the object the light hits is irrelevant.
edit: so as long as you aren't shining it out a window, you will be heating the room with the full wattage.

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4. ### rjain Golden Member

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The law of conservation of energy tells us that all the electricity must be converted to some other energy. All this energy will probably turn to heat in the case of a light bulb. A bulb that converts electricity into 100% visible light, however, will produce very little heat even if you want a very bright light.

The problem is that typical incandescent lights produce huge amounts of infrared light. Something like less than 20% of the light produced is visible. (Halogen lights are just a tweak to allow the filament to be much longer lasting and tolerate much higher amounts of power.)

Personally, I would rather build a computer (well, probably 3 or 4) that takes 1KW.

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5. ### CTho9305 Elite Member

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The point is, when the light hits your retina, the walls, etc, it ends up being converted back to heat.

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6. ### ZeroNine8 Member

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I couldn't find any good data, but from what I was able to find on google, incandescent bulbs are about 10% efficient and halogens are about 15% more efficient than incandescents (or roughly 11.5% efficient). So basically you're still converting 85-90% of the energy directly to heat, and your 500W halogens should be roughly equivalent to 425-450W heaters plus any of the light that is absorbed and converted to energy (may or may not be significant).

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7. ### Pudgygiant Senior member

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Yes, I agree with rjain, if you want a functional space heater, get an old quad rackmount ppro server. Those things give off so much heat I could cook burgers on them.

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8. ### wacki Senior member

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Me like this idea.

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9. ### NeoPTLD Platinum Member

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Two 500W halogen lamps:

watt=J/s. 1000J/s * 3600seconds/hr= 360,000J/hr=3,600KJ/hr

1,000W space heater:

watt=J/s. 1000J/s * 3600seconds/hr= 360,000J/hr=3,600KJ/hr

Lightbulbs put out a considerable amount of energy in form of IR radiation and if you let it go out the window or let it get absorbed by something like a wall, it won't make an effective heater.

All energy will turn into heat eventually.

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