Lamps Essex Junction VT
Which Lamps are Champs
It's Saturday morning, and like any other good homeowner, you are off to the local mega-hardware/lumber/appliance/flooring store to buy something for your weekend project. If your store is set up like mine, the very first products you see walking in the door are the light bulbs. This arrangement isn't by accident. The floor plans of these stores are carefully designed to promote sales, so one must conclude that light bulbs are big business. They are - last year, an estimated 1.3 billion "medium socket" bulbs were sold in the United States. Alas, most of these purchases are of lamps only an Enron executive would like. (A lamp, in the jargon of the lighting industry, is what you and I call a light bulb. A luminary is what you and I call a lamp or light fixture.)
The typical 100-watt lamp in your reading luminary is an expensive, energy-guzzling and wasteful product. It also accounts for something like 98 percent of all lamp sales. This is unfortunate, both for our environment and your bank account. An average suburban home contains around 40 to 50 individual lamps. Replacing them with energy-efficient models would reduce your electrical consumption by 7 to 8 percent, with savings of over $100 to $200 per year. Not bad for simply replacing some lamps. Homeowners' resistance to energy-efficient lamps is easy to understand - what product could be more low-tech than a light bulb? Yet lamp technology is a rapidly evolving field. New solid-state, compact-fluorescent, halogen and metal-halide lamps are all poised to replace the incandescent lamp. That bulb that Edison patented suffers many shortcomings. Given that these shortcomings are the result of the fundamental laws of nature, it's hardly surprising it took almost a century for these solutions to emerge.
We'll look at four types of lamps, from the oldest incandescents to the newest light-emitting diodes (LEDs).
Incandescent Lamps The type-A incandescent lamp is the light bulb we all know well. It works on a pretty simple principle: Hot things glow. In the lamp, an electric current passes through a resistive tungsten filament, heating it to more than 3,000° Centigrade. At this temperature, the metallic filament emits a yellowish-white light, a good approximation of natural sunlight. The filament would immediately oxidize, or burn up, if run in air, so the interior of the bulb is filled with a dollop of inert gasses like argon or nitrogen. These are very simple and incredibly inefficient devices. Most of the light emitted by a type-A lamp is actually heat. This shouldn't come as much of a surprise, at least to anyone who has tried to unscrew a working lamp, but the numbers are remarkable: A whopping 90 percent of the energy consumed by the lamp is wasted as heat, and only 10 percent goes to making light we can actually see. The amount of light (as opposed to heat) a lamp produces is given by its luminosity, not its wattage. Wattage is the power (energy/hour) consumed by the lamp. One can find type-A lamps rated at 15 to 300 watts. The ratio of luminosity to wattage is the efficiency, and is the true measure of light produced per dollar. Expect a ratio of 17 for type-A lamps. Thus, a 100-watt lamp will produce 17x100, or 1700 lumens. No other lamp has such a low efficiency! Running that 100-watt lamp 12 hours per day will cost most U.S. residents about 10 cents a day. The tungsten used in the filament is heated nearly to its melting point during use. Over time, the metal evaporates, plating the interior of the bulb with an atomically thin coating of metal. After approximately 750 hours of use (the "lifetime" listed on the lamp's packaging), evaporation will have eaten its way through the filament and it will break. "Long-life" lamps use a thicker filament and run at a lower temperature than normal lamps, so it takes longer for them to melt and break. While most sources describe long-life lamps as less efficient than normal bulbs, this is not reflected in luminosity data. There are also some sources that claim either high-wattage or lower-wattage lamps are more efficient than the other. This is also difficult to see from luminosity data. Clearly type-A lamps must have something going for them, or they wouldn't sell so well. They are inexpensive, at least to buy, with an average price of around 25 cents. They also produce a pleasing, natural color, much like that of natural sunlight. The Color Rendering Index measures this "naturalness." It runs from 100 for a lamp that reproduces sunlight perfectly, to lower values, such as 10, for those low-pressure sodium vapor lamps on interstate highways that make everyone look like little green people from Mars. Type-A incandescents have CRIs greater than 95. Those interested in more efficient incandescent lamps have options. For use in recessed lights, choose reflector lamps. type-R or type-BR lamps contain reflectors that redirect light out the front of the bulb. Expect to pay $5 per lamp for these bulbs. Choose parabolic aluminized reflecting lamps (type-PAR) or ellipsoidal reflector (type-ER) for twice the efficiency - and cost - of the other reflector lamps. Halogen lamps are also a more efficient incandescent choice. Normal lamps have low-pressure inert gasses in the bulb, which allows the tungsten filaments to evaporate. Halogen lamps, on the other hand, have halogen gasses in the lamp. Halogen gasses, like fluorine, are extremely reactive. Any tungsten that evaporates from the filament reacts with the fluorine and is redeposited onto the filament. Such filaments run at much higher temperatures, so they produce more visible light per watt of power. Their downside is the temperature of the bulb. These get so hot, normal glass would melt, so manufacturers use pure quartz instead, which has better thermal properties than regular glass. Do not touch the bulb when installing it, use gloves or paper toweling to shield the lamp from the oils and salts on your fingers. If any of these get on the bulb, they will produce hot spots on the silica glass, and the resulting thermal stress could break the glass. As in all of the incandescent options we've discussed, halogen lamps typically cost more than type-A lamps. These initial costs are generally offset by lower operating costs, particularly for halogen lamps.
Fluorescent Lamps When you think of today's fluorescent lamps, don't think about those flickering, yellow lamps from your elementary school days. While their up-front cost is greater than incandescent lamps, modern fluorescent lamps are significantly more efficient and longer lasting. They are also now available in compact sizes you can use in most residential luminaries. Fluorescent lamps have two parts - the tube and the ballast. The tube holds a miniscule quantity of mercury vapor and an inert fill gas, while its inner surface is lined with a phosphor. When the lamp is turned on, the ballast sends a high-voltage current into the tube, exciting the mercury atoms. The excited atoms emit ultraviolet radiation, which is absorbed by the phosphor. It, in turn, emits light in the visual range. While a small part of the ballast is heated to a high temperature, fluorescent lamps avoid the heat loss associated with incandescent lamps, so they are inherently more efficient and cost-effective than type-A bulbs. Before 1979, residential use of fluorescent lamps was limited to utility rooms and garages. Those long-bulb lamps have wonderful efficiencies (over five times those of type-A lamps), but they give off a nasty color light with a CRI of around 62, not what you want to light your home. But in 1979, compact fluorescent lamps (CFLs) were introduced in the United States. These innovative lamps were designed for use in standard residential luminaries: They have the usual screw-in base, a relatively compact size and a decent CRI. Best of all, they have high efficiencies and long lifetimes. They offer a cost-effective replacement for type-A lamps. CFLs are efficient because they lack the energy-hogging filaments of type-A lamps. More of the energy goes into making light (as opposed to heat) and that allows engineers to reduce the power consumption. Replacing a type-A lamp with a CFL can save substantial energy and money. Other advantages of CFLs make them even more attractive. Because they lack a fragile filament, CFLs last 10 to 15 times longer than type-A lamps. In typical use, an incandescent lamp might last 750 to 1,000 hours, while a CFL lasts from 6,000 to 10,000 hours. At 6 hours of use per day, that's 3 to 5 years between replacements of a CFL! During that time, you'd expect to install 10 incandescent bulbs. This lifetime comes at a price - CFLs cost $10 to $15 per bulb. This expense begs the question: Are CFLs a prudent investment? A handy calculator (www.eren.doe.gov/buildings/buying_elec.html, click on "lighting worksheet") allows you to determine for yourself. Assume you will replace a 100-watt type-A incandescent lamp with a 750-hour lifetime with a 25-watt CFL with a 10,000-hour lifetime. The lamps cost 50 cents and $14 respectively. Plug the numbers into the calculator, and you'll find that over the lifetime of the CFL, you'll save over $50. That's roughly $7 per year - for one lamp! For a typical house with dozens of lamps, the annual savings may well be over $100. Don't go running out and replacing all your lamps at once. CFLs have some weaknesses, too. Most annoying to many users is the time it takes the CFL to light. Most CFLs take a few seconds to light up, longer in colder weather. CFLs with instant and rapid-start ballasts are available, but they are somewhat more expensive and have shorter lifetimes than normal CFLs. Like all fluorescent lights, the ballast in CFLs contains coated electrodes. This coating partially evaporates each time the light is turned on; frequent cycling of CFL reduces its lifetime. Because of these two effects, CFLs are ill-suited in areas that need only brief periods of light. In other words, type-A lamps are perfectly fine for lighting closets and utility rooms. CFLs also suffer from "non-ideal" color, with the best scoring 85 CRI. Recall that large fluorescent lamps have a CRI of 62, while incandescents rate 95 or better. CFLs are probably a poor choice for lighting a bathroom mirror, for example, but would be fine in a large, light-colored room, such as a living room or kitchen. Remember, too, that CFLs make a more diffused light than incandescent lamps do. Finally, only CFLs with electronic ballasts can be set up on a dimmer switch. Most CFLs come with magnetic ballasts, and so can't be dimmed. Despite these drawbacks, CFLs have enough features to warrant their use in many residential settings. In the last three years, Californians have increased their purchases of CFLs sixfold, no doubt in response to the ongoing energy crisis there. CFL sales nationwide have tripled in the same time period. CFLs are a mature technology, and so are finally being adopted by the residential market.
High-Discharge Lamps High-discharge lamps (HIDs) include many rapidly evolving lighting systems, including mercury-vapor, metal-halide and high-pressure sodium lamps. Although mostly used in exterior and commercial settings, expect metal halide to develop into a niche product for interiors. HID lamps operate in a similar way to fluorescent lamps: A ballast unit introduces a high-voltage electric arc into a tube filled with mercury vapor and an inert gas. At their high operating temperatures (much higher than fluorescents), the pressure in the gas is so high the ultraviolet light emitted by the mercury atoms is absorbed by the inert gasses or other mercury atoms, which re-emit visible light. This light is very blue and very bright. Mercury-vapor lamps are common as street and gymnasium lights. They aren't a great choice for any residential application, because they have a low CRI and low efficiencies (roughly twice that of incandescent lamps). Metal-halide lamps, on the other hand, have great potential.
Except for the addition of iodine or another halide element to the mix of gasses in the tube, metal-halide lamps are similar to mercury-vapor lamps. They are about five times more efficient than incandescent bulbs and have CRIs from 65 to 90. Disappointingly, efficiency and CRI are negatively correlated - the best rendering lights are the least efficient. Expect to pay $20 per lamp, but they are extremely long lasting and amazingly bright - a 32-watt halide puts out as much light as a 150-watt incandescent. The high temperatures and pressures in the lamps demand use of special-purpose light fixtures for these bulbs. Metal-halide lamps have a downside for residential uses. Like all ballasted lamps, it takes a while for a halide bulb to turn on, often as long as three to five minutes. The bulbs can only turn on when the gas pressure is low, so after they're extinguished, they must cool for 10 to 20 minutes before they're restarted. Unlike the other lamps we've discussed, the color of metal-halide lamps changes slowly but significantly over the lifetime of the lamp. If color integrity is crucial, try combining halide and fluorescent lights. All lamps lose brightness over their lifetimes, but halides lose as much as 50 to 60 percent over their 10,000- to 20,000-hour lifetime. These bulbs produce a great deal of UV light, so they can bleach materials in a room. Coatings on the lamp can absorb this UV light, but it is best to read labels carefully. Finally, halide lamps are very particular about the orientation in which they run. Incandescent bulbs will run if they are pointing up, down, sideways, even on a moving platform, like a merry-go-round. Not so with halide lamps - they can be run only in certain orientations. Some are designed to run base up (given by the code BU), base down (BD), horizontally (H) or in a universal position (U). Again, careful package reading is essential.
Solid-State Lighting SSL is a generic term for a variety of lights that include semiconductor lasers and LEDs. Don't laugh! Like most people, you probably think of LEDs as the blinking red lights on old computers or children's toys or on your DVD player. But LEDs may well be the light source of the future. They are tiny, extraordinarily efficient and mechanically strong. They are also monochromatic - a given LED emits only one wavelength of light. Over the past decade, researchers in Japan, the United States and Europe have developed red, orange, amber, green and, most importantly, blue and ultraviolet LEDs. This color range means different LEDs can be mixed to produce any color light, including white. Unlike all of the other lamps we've examined, LEDs produce light without the use of a heated element or gas. Instead, they are based on the semiconductors so common in today's digital age. Each LED is a sandwich of metallic layers, some with an excess of electrons (the "N-type" layer) and some with a deficit of electrons (the "P-type" layer.) When the sandwich is given an electric charge, the electrons in the N-type layer and the holes in the P-type layer flow toward the junction of the layers. There they combine electrically and, in the process, emit light of one particular color.
This is an efficient light-producing mechanism, with the best LED having efficiencies well above seven times that of incandescent lamps. LEDs are the "not-ready-for-prime-time" players of lighting systems. They will be, though. They are far too efficient and far too amenable to digital control to not become a mainstay form of lighting. But don't put off any home projects while you are waiting - residential LEDs are at least 10 to 20 years off. However, they have found a current growth market in traffic signals and automobile brake lights. In the meantime, when you next walk into your local mega-hardware store, take a few minutes to look at the array of lamps available for residential use. Most shoppers automatically reach for the good old type-A lamps, and changing habits is undoubtedly difficult. But try installing a few CFLs in those hard-to-reach lighting fixtures. Most people will find it very easy to break the habit of frequent bulb replacement and enjoy the cost savings, too. Larry McKenna, Ph.D. is president of Working Knowledge Inc. in Overland Park, Kansas.