How to Choose the Right Light

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You can save money and help the environment by choosing the right light bulbs.

The electric light bulb, one of the most essential electric devices in the average home, may also be the most ignored. Most people think about them only when one burns out. But, in fact, carefully choosing the proper lamp—a less common but more accurate term than light bulb—for your home can help reduce your energy consumption as well as lower your electric bill and the amount of money you spend on replacement lamps. Using energy efficient lamps, which need not be replaced often, can also reduce the amount of trash piling up in landfills. And, by using less electricity, consumers can help reduce the amount of pollution entering the atmosphere from electric power plants.

In 1993, consumers seeking energy efficient lamps had a new choice—the electronic lamp, or E-lamp. The E-lamp uses only 25 percent as much electricity as a standard incandescent lamp and will last for 14 years if lit for four hours a day, according to its developers.

Types of lamps

Most lamps are classified as either incandescent or gaseous discharge lamps. Standard incandescent lamps, pear shaped lamps typically found in table lamps, are the most common type of incandescent lamp. A less common incandescent used in the home is the tungsten halogen lamp. Such lamps include the tiny, intense lamps used in some newer indoor fixtures. Higher wattage tungsten halogen lamps are used in patio lighting and outdoor spotlights.

Fluorescent lamps are the most commonly used gaseous discharge lamp. Linear fluorescents are long tubes often found in kitchen fixtures and widely used in schools and offices. A recent addition to the fluorescent family is the compact fluorescent lamp, which can be used as an energy efficient replacement for standard incandescents.

Incandescent and gaseous discharge lamps differ in the way electric current is passed through the lamp. Incandescent lamps light up when electricity passes through a thin wire called a filament. As the filament heats up, it begins to incandesce (glow). Along with a filament, an incandescent lamp consists of a glass enclosure called a bulb, supports that hold the filament, and a base that makes contact with an electric power source. Over time, the filament, which is usually made of tungsten, evaporates. Eventually, the weakened filament breaks, and the lamp burns out. To lengthen the life of the filament, the bulb is filled with a mixture of nonreactive gases, usually argon and neon, that slow the filament’s evaporation.

Standard incandescents are popular in part because they give off light that brings out red tones. As a result, walls and other objects—including pale skin—appear warmer. Incandescents’ greatest appeal, however, may be their low purchase price, usually less than $1.

But standard incandescents are a fairly inefficient way to light your home because they last for a relatively short time—about 750 hours—and because only about 10 percent of the electrical power they use is transformed to visible light. The rest is wasted as heat. And standard incandescent lamps darken over time, as tungsten evaporating from the filament leaves a dark deposit inside the bulb. This deposit gradually reduces the amount of light given off.

Tungsten halogen lamps

Loss of light is less of a problem with tungsten halogen lamps, which contain a small amount of iodine vapor in addition to argon and neon gas. The iodine vapor combines with the burnt off tungsten that has evaporated from the filament. When the combined iodine and tungsten touch the hot filament, the tungsten sticks to the filament. The iodine then recirculates to combine with more evaporated tungsten. These substances reduce the dark deposit on the inside of the lamp. As a result, tungsten halogen lamps produce more light over their lifetime than do standard incandescents. In addition, they may last almost twice as long under ordinary conditions. But their purchase price is up to 15 times higher.

Tungsten halogen lamps are also much more fragile than are standard incandescents. In fact, they may explode if not handled with care. An explosion may occur, in part, because the gas in the bulb is pressurized. Pressurizing raises the temperature within the bulb so that when it is lit, the iodine and tungsten can combine. In addition, tungsten halogen lamps are made of quartz rather than glass to withstand the higher temperatures. If you touch the quartz bulb, the oil from your fingertips will interact chemically with the quartz when the lamp heats up, weakening its ability to contain the gases within. For this reason, packages containing these lamps usually contain a plastic glove to be used when changing them. Because of their potential for failure, tungsten halogen lamps are best used in enclosed fixtures such as wall sconces.

Gaseous discharge lamps

Gaseous discharge lamps rely on gas rather than a filament to transmit electric current through the lamp. The two most common types of fluorescent lamps—linear lamps and compact fluorescent lamps—contain mercury vapor and argon gas. Both of these lamps consist of a glass tube; metal enclosures for the ends of the tube; a connection to the power source; an electrical device called a ballast, which provides voltage to start the lamp and helps regulate the flow of current; and devices called cathodes at each end of the tube. The cathodes are coils of tungsten covered with chemicals that easily give off electrons, negatively charged subatomic particles.

As an electric current passes from one cathode to the other, the electrons shoot through the mercury vapor. The collision of the electrons with the mercury vapor causes the mercury atoms to release invisible ultraviolet rays. These rays are absorbed by phosphors, chemicals that coat the inner surface of the tube, which then glow or fluoresce, producing visible light.

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Compact fluorescent lamps are smaller than linear fluorescents, and some are available with a screw-in base that contains a ballast. The screw-in base is the size of an incandescent base so that the lamp and ballast unit can be used in incandescent lamp sockets, such as the socket of a table lamp.

The new E-lamp, like a fluorescent lamp, produces visible light by the action of ultraviolet rays on an inner coating of phosphor. In this case, however, ultraviolet energy is created by high frequency radio waves emitted by a tiny antenna inside the bulb. The radio waves cause the mercury vapor inside the bulb to release ultraviolet energy that acts on the phosphor to produce visible light.

Evaluating incandescents

The label on a lamp’s package will provide you with the information you need to calculate how energy efficient it is compared with other lamps. By federal law, the package labels for incandescent lamps must list the amount of light the lamp gives off, expressed in units called lumens; the amount of electricity the lamp uses, expressed as watts; and the average life span of the lamp, expressed as rated hours. Similar information may appear on fluorescent lamp packages, though not mandated by law.

One measure of a lamp’s energy efficiency is its lumens per watt (LPW). The LPW compares the amount of light a lamp produces to the amount of electricity it uses. The higher the LPW, the less energy is used to produce a given amount of light. In other words, lamps with a high LPW rating give you more light for your energy dollars.

You can calculate a lamp’s LPW rating by dividing its lumen rating by its rated wattage. A 60-watt incandescent lamp, which typically gives off 870 lumens, has an LPW of only 14.5. In contrast, a 40-watt fluorescent lamp, which converts more of its electric energy to visible light, is rated at 3,150 lumens and, therefore, has a LPW of 78.8 at least five times higher than a 60-watt incandescent.

A second measure of a lamp’s cost effectiveness is how often it must be replaced. A typical 60-watt incandescent has an average life of 750 hours. In comparison, a fluorescent lamp is rated to last 20,000 hours.

Incandescents marketed as “long life” or “energy efficient” lamps do, in fact, last longer and consume less electricity than standard incandescents do. But studies have shown that they create this saving by giving off significantly fewer lumens. Such lamps produce less light than standard incandescents do for the same amount of electricity consumed. “Soft white,” pink, or other coated incandescents also produce less light than do clear incandescents because the coating absorbs some of the light.

Choosing a fluorescent

Among fluorescents, energy efficiency depends on the colors produced by a lamp. “Deluxe cool white” and “deluxe warm white” fluorescent lamps may make red surfaces look more natural than they would under the light of ordinary “cool white” fluorescent lamps. But you pay a price for the more natural color appearance. Cool white lamps produce about 1.4 times more lumens than do deluxe cool white or deluxe warm white lamps.

Because they are so energy efficient, compact fluorescent lamps may be a good replacement for standard incandescents. A 7-watt compact fluorescent lamp produces 400 lumens, for example, about half the lumens as one 60-watt incandescent lamp. But two 7-watt compact fluorescents will use only about 36 percent of the energy consumed by a single 60-watt incandescent. And although the purchase price of compact fluorescents is about 15 times higher than that of standard incandescents, the fluorescents last approximately 10 times longer. Because they do not have to be replaced frequently, they cost significantly less to use over their lifetime.

The E-lamp has the benefits of its fluorescent cousins. A 25-watt E-lamp has an LPW of approximately 70, about 5 times higher than that of a standard 60-watt incandescent, according to the lamp’s developer. Such a drop in electricity consumption would produce substantial savings.

Calculating lamp costs

Experts report that a higher purchase price sometimes discourages consumers from buying more energy efficient lamps. But purchase price is only one aspect of a lamp’s price to consider. To calculate the cost of buying and using a particular lamp—for example, a 60-watt incandescent—first determine your basic electric rate by dividing the total amount of your monthly electric bill by the kilowatt-hours (kwh) used. (The average rate per kwh in the United States is 8 cents.) Then multiply the rate per kwh by the rated wattage of the lamp, in this case $0.08 multiplied by 60 = $4.80. This result is the cost of operating a 60-watt lamp for 1,000 hours.

Next, find the cost of the lamp itself over the same time by dividing the rated hours by 1,000 (750 1,000 = 0.75) and then dividing the cost of the lamp by the result ($0.89 0.75 = $1.19). Finally, add this number to the cost of operating the lamp ($1.19 + $4.80 = $5.99). The sum is the true cost of using an 89 cent incandescent lamp for 1,000 hours.

In contrast, the cost of buying and operating an 18-watt fluorescent and its ballast, which provide an equivalent amount of light, is about $1.63. The cost for a 7-watt compact fluorescent lamp is about $1.90. Experts say that such significant savings—coupled with the sharp reduction in the amount of energy used—should provide consumers with a strong incentive to consider lamps other than the familiar incandescent.

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