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Noon Edition

Heated Differences

Why do regular incandescent light bulbs get hotter than fluorescent bulbs?

An incandescent bulb becomes too hot to touch soon after you turn it on. A fluorescent bulb, on the other hand, takes several minutes to warm up, and never feels really hot. What's the difference?

When you flick on a light with a regular incandescent bulb, electricity is converted to heat in the tiny, tungsten wire inside. In a 75-watt bulb, the wire heats up to about 4600 degrees Fahrenheit! At such a high temperature, the energy radiating from the wire includes some visible light. Incandescent light bulbs aren't the most efficient light source, though, because 90% of the electricity they use produces heat, while a measly 10% produces light.

Fluorescent bulbs are designed to produce light without so much heat. Forty percent of the electricity they use produces light, which might not sound so impressive unless you compare it with incandescents.

When you turn on a fluorescent light, electrons collide with mercury atoms inside the bulb, producing ultraviolet light. We can't see ultraviolet light, so there's a thin layer of phosphor powder inside the bulb to convert the ultraviolet to visible light. Fluorescent bulbs stay cooler because this process produces much less heat to begin with, and because their bigger size helps disperse heat more quickly.

What do these heated differences mean for energy efficiency? A regular incandescent light bulb uses about four times as much energy as a fluorescent bulb, to produce the same amount of light.

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