How to Calculate the Real Power of Fluorescent Lights

Written by bill brown
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How to Calculate the Real Power of Fluorescent Lights
CFLs are more powerful, watt for watt, than incandescent bulbs. (Cfl fluorescent lightbulb on dark background image by Silverpics from

Compact fluorescent lamps, or CFLs, are being used more and more as they save money and energy. They are usually around four times as efficient as incandescent bulbs, creating the same amount of light with only 25 percent of the energy. There are slight variations from brand to brand, but you can calculate the real power of a fluorescent light by multiplying the wattage of the bulb by the amount of light produced (in lumens) per watt.

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  1. 1

    Find out the wattage is of your fluorescent bulb. For CFLs, the wattage it is printed on the plastic housing of the ballast. On tube lights, it is printed directly on the bulb.

  2. 2

    Multiply the wattage of the bulb by 70 for a CFL and by 80 for a four-foot tube fixture. These numbers represent the approximate lumens per watt produced for each type of bulb. For a 13 watt CFL, the real power of the light is about 910 lumens. For a 40 watt, four-foot tube fluorescent, the result is about 3,200 lumens.

  3. 3

    Record the data and repeat for each of the fluorescent lights you are measuring.

  4. 4

    Sum the total of the lumens produced by all the fluorescent lights to get the total power of the lights.

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