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Ask Mr. Tight-Watt: Incandescent Light Bulbs   Smart Choices Archive

Ask Mr. Tight-Watt: Incandescent Light Bulbs

See the light on incandescent light bulbs.

Ask Mr. Tight-Watt

Mr. Tight Watt answers a question from a Smart Choices reader.

Question: What is the efficiency rating for a 60-watt incandescent bulb? From Olga

Answer: There are various ways of defining “efficiency;” that’s what we’ll try to do here.

First, remember that like any electrical device, an incandescent light bulb is nearly 100 percent energy efficient. That is, nearly all of the energy coming into the light bulb is used in some way; it is not destroyed or lost, although some may become unavailable for further use.

So while the quantity of energy is the same, the quality may be different. Light bulbs, for example, don’t use all of their energy as light. Incandescent bulbs use electricity to produce only about 10 percent light; the remaining 90 percent of their output is as heat. That’s not a very efficient use of a light bulb! Compact fluorescent bulbs (CFLs) on the other hand, produce only about 30 percent heat and 60 percent light.

To determine energy use and savings of various types of bulbs:

  1. Look at the lumens/watt ratio for any bulb to see how much light you get from the bulb. A lumen is a measure of light and wattage is a measure of power, or energy consumed per unit of time, according to Energy Star. A 60-watt incandescent bulb takes 60 watts (energy consumed) to produce 800 lumens of light. An equivalent 13–15 watt compact fluorescent bulb (CFL), on the other hand, takes only 13–15 watts to produce that same 800 lumens of lighting. Think of it in terms of a “miles per gallon” analogy, with the watts as the amount of “gas” it takes to “travel” to the number of lumens.
  2. Look at the lifespan of the bulb. Because of the raw materials used to manufacture light bulbs, you save energy by buying bulbs with a long life. The average life of an incandescent bulb is only 1,000 hours, while a CFL averages 9,000 or more (some new CFLs can go 30,000 hours!). While you pay a bit more for CFLs (the cost has come down dramatically, however), you are using up considerably fewer resources with your purchase.
  3. Think about your personal energy efficiency in replacing bulbs. Especially in hard-to-reach spots, installing a bulb that has to be changed only every few years makes better use of your time (and less risk of falling off the ladder!).

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