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Due to an experiment, I need a small heater (around 70 to 100 watts). I intend to use an incandescent bulb so it can act as a heater. What I wonder here is will a 70 watts Incandescent Bulb be equal to a 70 watts heater?

Xitrum
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2 Answers2

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From Wiki:

Approximately 90% of the power consumed by an incandescent light bulb is emitted as heat, rather than as visible light.

So, yes, the incandescent bulb can be used as a heater and, in fact, has been used as a heater. For example, see: Easy-Bake oven.

The original toy used an ordinary incandescent light bulb as a heat source

Alfred Centauri
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  • would an electric Heater at 70 watts emit more than 90% of the power consumed as heat? – Malachi Jul 31 '13 at 14:12
  • @Malachi, "Electric resistance heating converts nearly 100% of the energy in the electricity to heat." http://energy.gov/energysaver/articles/electric-resistance-heating – Alfred Centauri Jul 31 '13 at 14:19
  • so then he would need a little more than a 70 watt lightbulb to be considered a 70 watt heater, right? – Malachi Jul 31 '13 at 15:09
  • @Malachi, that's correct. – Alfred Centauri Jul 31 '13 at 15:33
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    If 90% is converted to heat then a 70 Watt bulb would produce ( 100/90 * 70 ) 63 Watts of heat. A 77.78 Watt bulb would produce 70 Watts of heat. Since they usually sell 60, 75 and 100 Watt bulbs the best bulb is probably a 75 Watt version. – Hennes Jul 31 '13 at 16:00
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Whatever bulb is used, basically all the power consumed will go into heating the environment, with the notable exception being any photons that escape through a window or some such thing.

Different styles of bulb have different visible light-heat ratios, but even the visible light emitted will simply bounce around the room a few times and deposit all its useful energy into random thermal motions. You know these photons cease existing, at least in the visible range, because when you turn off a light, the room essentially instantly goes dark.

Incandescent bulbs work better at heating than, e.g., certain fluorescent bulbs for a given amount of visible lighting because they consume more power (and thus emit more direct heat) per unit desired light. However, even if you designed a light bulb that emitted 100% of its photons in the visible range, that power (small though it would be) would all go into heating its environment.