Shedding Light on Picking Fluorescent Bulbs

QUESTION: When shopping for light bulbs, I usually just look for the wattage I want. With compact fluorescent bulbs, though, the wattage is much lower and doesn’t compare with common incandescent bulbs. 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?

ANSWER: You have to consider several factors when choosing a compact fluorescent lamp to replace an incandescent bulb. Finding a good fit is often the main concern, 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.” Unfortunately, lumens are not always prominently displayed on the bulb package. The Federal Trade Commission is trying to change this and has adopted labeling requirements for many common incandescent bulbs and one-piece fluorescent lamps.

The new rule requires lumens and watts to be displayed on the package with equal prominence. All products manufactured after Dec. 1, 1995, must have the new labeling, though products with old packaging may continue to be sold. 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 fluorescent lamp produces 1,200 lumens, the same as a 75-watt incandescent bulb. You might assume that the same amount of light comes from the fluorescent lamp once you’ve screwed it into your table lamp, right? Actually, fluorescent lights are more sensitive to temperature and lamp position than incandescent sources. This means you’ll get less light if you use a fluorescent lamp 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 fluorescent lamp in a table lamp with the base down will give you less light than installing the same fluorescent lamps in a ceiling fixture with the base up. A related issue with table lamps is that the base of many fluorescent lamps 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).

The bottom line is this: Even if the packaging indicates equal lumens, you may appreciate a higher wattage fluorescent lamp product because of unavoidable temperature or position effects. But don’t be discouraged--fluorescent lamp technology is improving all the time, both in terms of increased brightness and reduced size. Watt for watt, fluorescent lamps produce three to four times as much light as an ordinary incandescent bulb. So, as a rule of thumb, you can replace an ordinary incandescent bulb with a fluorescent lamps that has one-fourth to one-third the wattage. But if used in hot or cold areas base down, or if the base may block some needed light, lean toward that one-third figure.

Written by Jack Brautigam from the Education and Information Network of the Washington State Energy Office.