New Light on Energy Conservation

Your local hardware store tries to sell you some new energy-efficient "compact fluorescent" light bulbs at $20 apiece, suggesting that you use them to replace your incandescent bulbs. Would you buy them?

Your local electric utility offers to give you - free - several of the same type of bulbs, telling you they will save you money on your electric bill. Would you accept them?

If you answered no to either of these questions, you're guilty of missing a chance to save yourself a nice chunk of your hard-earned money while helping the rest of us by saving energy, conserving natural resources, decreasing air pollution, reducing acid rain, and slowing down the growth of global warming.

These new light bulbs - known as "screw-in" or "compact" fluorescent bulbs - have been around since the early 1980s, but until recently they were difficult to find in Iowa. A recent survey of retail stores in central Iowa, however, located bulbs made by General Electric, Lights of America, Osram, Panasonic, Philips, Satco, Sylvania, and Westinghouse. Unfortunately, too few homeowners are purchasing them.

Fluorescent light bulbs - first introduced in 1939 at the New York World's Fair - have long been popular in stores, offices, and other commercial buildings. For the same amount of light, they use only about one-fourth as much electricity as incandescent bulbs and produce only about one-fourth as much heat, leading to lower air conditioning bills. But fluorescents have not been popular with homeowners, who found they had too many disadvantages: they needed their own, extra large fixtures, they were too noisy, they often flickered annoyingly, they were oddly colored, and they took several seconds to light.

The best of the new compact bulbs demonstrate that all these problems have been solved:

There are several styles of compact fluorescents. All basically consist of one or two relatively thin fluorescent tubes bent into a narrow U-shape. In some bulbs these tubes are bare and visible to the eye, while in others they are encased in a frosted globe or a plastic cylinder. The latter are much more attractive, and most persons regard them as more attractive than incandescent bulbs and easier to view directly. Some of the bulbs have a ballast separate from the tube, so that only the tube needs to be replaced when the lamp burns out.

The main advantage of the compact fluorescent bulbs is that they require only about 20 to 25 percent of the electricity of ordinary incandescent bulbs. Compact fluorescents in the 9 watt, 18 watt, and 25 watt sizes provide approximately the same amount of light as 40 watt, 75 watt, and 100 watt incandescent bulbs. For example, the 18-watt Philips SL18 bulb provides 1100 lumens (a measure of visible light) compared to 1150-1180 lumens for 75-watt incandescents, and in a side-by-side visual comparison viewers are unable to detect which is brighter.

The savings in electric energy translates into significant dollar savings. As shown in the table below, the dollar savings over the lifetime of a compact fluorescent may be enough to pay for nearly two new fluorescents.

The rated lifetime of the compact fluorescents is typically 10,000 hours, compared to 750 hours for incandescents, meaning about 13 incandescents must be purchased to last as long as one fluorescent. Do the bulbs really last as long as claimed? One fluorescent left on continuously in a hallway has lasted well over a year, over 10,000 hours. In another side-by-side test begun last November, two bulbs were left on continuously except for being switched on and off several times daily. The incandescent bulb with a claimed lifetime of 750 hours lasted 800 hours, while the fluorescent has now lasted over 5,000 hours.

One notable advantage of the compact fluorescents is that they run much cooler. During the first few minutes it is on, the compact fluorescent bulb remains cool to the touch, while the incandescent quickly becomes too hot to touch. After the compact fluorescent bulb has been on for a long time it typically feels warm but hot to the touch, and can often be handled with bare hands without discomfort.

The compact fluorescent bulbs do have some disadvantages, fortunately minor ones. They tend to be larger than the corresponding incandescent bulb, so they will not fit in some fixtures. In one central Iowa house with 35 incandescent fixtures, the compact fluorescent bulbs were found to fit in 29 of the fixtures, but were too long for the other six.

Another disadvantage is that the compact fluorescent bulbs run somewhat dim in cold weather, so they may be unsuitable for use in outdoor lights or in unheated garages or other spaces. However, they work well in heated spaces.

How much would be saved in a home by replacing all incandescent bulbs with compact fluorescents? It clearly depends on the amount of lighting used by the occupants. In a home in which an average of ten 100-watt bulbs are left on for an average of 5 hours a day, the savings would amount to about 1350 kilowatthours each year - approximately $100 worth of electricity.

In some parts of the country, utilities have been giving compact fluorescent bulbs away. The reasoning is that it is cheaper for the utility save one watt of power plant capacity by purchasing these bulbs than to build one watt of capacity. Knowledgeable homeowners have been eager to accept the bulbs, but some persons refuse them because they believe the utility is trying to trick them. Until recently, most Iowa utilities did not promote these bulbs to their customers, a notable exception between the municipal utility at Osage. In Osage, homeowners who allowed the utility to put a load management device on their air conditioner could receive two free compact fluorescents, and any customer who bought a fluorescent from a local supplier could receive a 50% rebate from the utility.

Don't pass up any incentives your utility might offer you to purchase the new bulbs. But if you wait for it to offer incentives, you will be wasting energy and money. And if you are looking for that elusive gift for a friend or relative who has everything, why not consider a compact fluorescent - the $20 gift that will be worth $50 to the recipient?

Here's a direct comparison of two popular light bulbs purchased in central Iowa:

                                  Fluorescent             Incandescent
Electric power                      18 watts                75 watts
Light output                      1100 lumens             1150 lumens
Efficacy (energy efficiency)        61 lumens/watt          15 lumen/watt
Price per bulb                     $17.55                  $ 0.69
Rated lifetime                     10,000 hours            750 hours

Cost for 10,000 hours of light:
Number of bulbs needed                 1                     13
Amount of electricity needed         180 kWh                750 kWh
Cost of bulbs                        $17.55                 $ 8.97
Cost of electricity at 7c/kWh        $12.60                 $52.50
Total cost of 10,000 hours           $30.15                 $61.47
Summary: Over its 10,000 hour lifetime, the compact fluorescent will save over $31, nearly enough to buy two new 18-watt compact fluorescents.



Copyright 1995 by Laurent Hodges, 12 Physics Hall, Iowa State University, Ames, IA 50011-3160
Last update: June 11, 1996
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