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“Attention, Wal-Mart Shoppers” (March/April) is the best, most comprehensive article I’ve read about compact fluorescent bulbs (CFLs). You eloquently explained the benefits and costs (mercury pollution, inadequate packaging) of CFLs. Thank you for writing this piece. I don’t shop at Wal-Mart, but I may find myself there the next time I need a CFL—in the cardboard packaging, of course!

Davina Marraccini

Smyrna, Ga.

We dispose of the long fluorescent tubes through our local borough services, in much the same way we dispose of batteries. Now, having read your story on Steven Hamburg, I will do the same with the many compact swirl-shaped fluorescent bulbs we use.

I disagree strongly with the claim that a 15-watt fluorescent bulb equals the quality and strength of light given by a sixty-watt incandescent bulb. I tried replacing the seventy-five-watt incandescent bulb in a walk-in closet with the stated compact fluorescent equivalent. It was as if the power had suddenly been usurped by a surge from some unseen appliance. We could no longer see objects clearly in this closet. We solved the problem by one-upsmanship. We inserted a 26w/100w CFL bulb (which theoretically equals a 100-watt incandescent bulb), and found that it did equate to our old seventy-five-watt incandescent. These bulbs are most certainly not equal. Good, yes; but as Mr. Hamburg states, “We’ve got a way to go on that one.”

As a user for years, I would advise consumers to purchase the daylight version and go up a notch in wattage when purchasing these bulbs. But by all means, do buy them.

Thanks to Wal-Mart and Mr. Hamburg for their vision. Now, I’d like to see him address the problem of plastic shopping bags—perhaps come up with a biodegradable version?

Geraldine Nelson ’51

Middlesex, N.J.

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Replacing the light bulbs in my house as described in “Attention, Wal-Mart Shoppers” unfortunately made this physicist think a bit about their significance. The article is indeed correct that incandescent bulbs emit only 10 percent of consumed energy as light, but the implied free lunch of replacing them with efficient fluorescent bulbs is largely illusory. Almost all the energy emitted by either bulb type is or ultimately becomes heat. In a heated building, that offsets heat generated by the building’s climate-control system. The net effect is not to save energy, but to reallocate some of the overall energy consumption to the source of the bulb’s electricity. Buildings are typically heated by natural gas, oil, or even electricity, which itself comes from those same sources (plus coal burning, nuclear reactors, and flowing water). Replacing incandescent bulbs has almost nil effect on the energy consumption of a heated building.

Counterintuitively, bright lighting in a heated house is not expensive or wasteful. Rather, it is an intelligent application of a dual-usage resource. That may either increase or decrease the energy costs for a building, but weakly, as the change depends not on local energy prices but on their differences.

Switching bulb types in an air-conditioned building does yield benefits, as a 75–80 percent drop in heat output reduces the need for cooling, which is very energy-intensive. But even this clear gain must be hedged; the biggest users of air conditioning are office buildings, which commonly have extensive fluorescent lighting already.

In addition, the times of day with the highest demands for cooling also have the most sunlight and the lowest demands for lighting; the benefits of replacement are moderated accordingly. Similarly, the times with the highest demands for heating also have the highest demands for lighting. Hence bulb usage has little effect on total consumption. Seasonal temperatures also reduce any benefits; air-conditioning demands, reduced by bulb replacement, typically last only part of a day during a few hot months. Heating demands, only marginally affected by replacement, are usually required full- or part-time for a large fraction of the year.

Demographics compound this disfavor, as the vast majority of the world’s light-bulb–using population lives in colder climates. Outdoor lighting would seem to reduce energy consumption with bulb replacement, but incandescent bulbs are not widely used outdoors, and the efficiency of the various other bulbs in common use is already superior.

Other topics that affect replacement benefits could be added—heat retention by buildings and humidity’s effect on comfort, to name two—but the fundamental things still apply. Nature associates heat with light and requires mammals to stay warm; market pricing tends to equalize the costs of different sources of energy; population demographics are skewed to favor heating. These are powerfully compensative for any purported benefits. In short, bulb replacement might be a kosher pickle or two, but sorry, it is no free lunch.

Andrew K. Gabriel ’76

Pasadena, Calif.

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