Ask Mr. Green: What Light Is More Efficient, Fluorescent or Halogen?

Hey Mr. Green,

My dad is an environmental scold and refuses to let my mother have a halogen lamp in her study because he claims it would waste energy and thereby contribute to climate change. Is he right, or just light years from the truth, as is often the case?

—Anna, in Berkeley, California

Father, at times, does know best. Contrary to urban legend (and to some manufacturers’ claims that halogen lighting is green), halogen lamps are nowhere near as energy-efficient as fluorescents. Even the best new halogens require about three times as much power as fluorescents. They do, however, consume around 25% less than the old-fashioned incandescents. Although halogens last two to four times longer than old incandescents, their life expectancy still is usually a lot shorter than fluorescent lamps. The only other lights that come near fluorescents’ efficiency are LEDs, as we’ve previously noted.

The easiest way to rate any lamp’s efficiency is to calculate the amount of light you get per watt of energy you burn. You take the number of lumens (light units) and divide it by the number of watts (hey, it’s just like computing miles per gallon for your car).

You can now find the ratings for these printed on bulb packages in a little chart headed “Lighting Facts.” If, for example, it says a lamp emits 820 lumens and uses 60 watts, then you’re getting 820/60 = 13.7 lumens per watt. If it says the lamp produces 870 lumens and needs 13 watts, then you’re getting 870/13 = 66.9 lumens per watt, or about four times as much light per watt — which is the difference between a fluorescent and an incandescent. (The chart also states the bulb's approximate operating cost and life expectancy.)

To give Mom a tutorial on more efficient illumination, send her to the EPA lighting site.

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