How Everything Works
How Everything Works How Everything Works

Question 511

How does the wattage of a candle compare to the wattage of a light bulb?
A 60 watt light bulb emits about 6 watts of visible light while wasting the remaining 54 watts of electric power as other forms of thermal energy. A candle probably also consumes about 60 watts of chemical energy (the paraffin wax) but emits much less than 3 watts of visible light. The light bulb is clearly not very efficient at converting electric power into visible light but the candle is even less efficient. That's because the candle flame operates at a lower temperature (about 1700° C) than the filament of the light bulb (about 2500° C) and the spectrum of light emitted by a hot object depends strongly on its temperature. The cooler flame emits relatively more infrared light and less visible light (particularly blue light) than the hotter filament.

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