Consider Many Factors When You’re Choosing Fluorescent Bulbs

Fri., Jan. 26, 1996

Amy Mickelson Washington State Energy Office

Q. When shopping for light bulbs, I usually just look for the wattage I want. With compact fluorescent bulbs, though, the wattages are much lower and don’t compare with common incandescents. All I have to go on is what the package says it should replace. Are these claims realistic? How can I be sure of picking the right bulb for the job?

A. Choosing the correct compact fluorescent lamp (CFL) to replace an incandescent bulb requires consideration of several factors. but getting the right amount of light is probably a close second. The secret is to compare lumens rather than watts. A lumen is a unit of light output, commonly associated with brightness, but unfortunately it is not always prominently displayed on the bulb package. The Federal Trade Commission adopted new labeling requirements for certain lighting products that include all newly manufactured one-piece CFLs. The new rule requires lumens and watts to be displayed on the package with equal prominence. Incandescent products also are required to comply with these new labeling requirements. The intent is to help consumers choose more efficient bulbs - those that give the necessary lumens but use fewer watts.

Say you’ve discovered that a 20-watt CFL produces 1200 lumens, the same as a 75-watt incandescent bulb. You might assume the same amount of light from the CFL once you’ve screwed it into your table lamp, right? Fluorescent lights are more sensitive to temperature and lamp position than incandescent sources. What this means is you’ll get less light if you use a CFL in unheated areas or inside enclosed fixtures, where heat tends to build up. You’ll also get less light if the bulb is installed base down rather than base up. For example, installing a CFL in a table lamp with the base down will give you less light than installing the same CFL in a ceiling fixture with the base up. A related issue with table lamps is that the base of many CFLs will block light in the downward direction, generally where it is most needed. The best solution might be to use a “circline”-type compact fluorescent. The circular-shaped tube will not block light in the downward direction and will not get in the way of most existing lamp harps (the part that supports the lamp shade).

Even if the packaging indicates equal lumens, you may appreciate a higher wattage CFL product due to unavoidable temperature or position effects. But don’t be discouraged. CFL technology is improving all the time, both in terms of brightness and size. Watt-for-watt, CFLs produce three to four times as much light as an ordinary incandescent, so a good rule of thumb is that an ordinary incandescent bulb can be replaced with a CFL that has one-fourth to one-third the wattage. However, if used in hot or cold areas, used base down, or if the base may block some needed light, lean toward that one-third figure.

For free factsheets on compact fluorescent lamps, call our Energy Hotline at (800) 962-9731 or 324-7980.

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