October 1, 2006
By Mary Beth Breckenridge
Even Thomas Edison would scratch his head over the choices in a typical home center's light bulb aisle.
The array seems endless -- compact fluorescent and incandescent, clear and frosted, Edison base and candelabra, round and funnel-shaped.
So many options, so little information.
We're here to help you sort out the myriad bulbs out there. For simplicity's sake, we'll stick to general-service bulbs (also called Edison-base bulbs), the screw-in types that fit most lamps and light fixtures in a typical home. That's where most of the decision-making comes in, anyway, because most other fixtures require highly specific bulbs.
Household bulbs fall primarily into three categories -- standard incandescent, halogen and compact fluorescent.
Standard incandescent is, of course, the bulb most of us know and use, essentially the kind Edison invented in 1879. It has a very thin tungsten filament, which heats and emits light as electrical current passes through it.
That works pretty well, but there are drawbacks, said Steve Goldmacher, director of corporate communications for Philips Lighting Co., and Joe Rey-Barreau, educational consultant for the American Lighting Association and a member of the faculty of the University of Kentucky College of Design.
For one thing, the tungsten flakes off over time, causing the filament to fail. For another, tiny bits of evaporated tungsten end up adhering to the inside of the bulb as carbon, dulling the bulb. And the bulbs are highly inefficient: Only 5 percent of the energy produced goes into light, with the rest producing heat.
Since Edison's time, other technologies have come along to improve on the standard incandescent bulb. One is the halogen bulb, which is another form of incandescent bulb that contains a gas to improve the functioning. The gas, which contains a bit of halogen, does a couple of things, Goldmacher and Rey-Barreau said: It produces an interaction that prevents the carbon from settling on the inside of the bulb, and it causes the bits of evaporated tungsten to jump back onto the filament, essentially allowing the filament to regenerate.
For that process to happen, however, the bulb needs to get very hot. That's accomplished by making the bulb smaller, which puts the filament much closer to the glass and concentrates the heat, Rey-Barreau said.
That's why most halogen bulbs you see are considerably tinier than a regular light bulb, and why halogens are so hot to the touch. Nevertheless, some manufacturers are encasing that tiny bulb inside a larger glass housing and mounting it on a screw-on base, producing halogen bulbs that can be used in standard lamps and fixtures without jeopardizing your skin.
A much bigger change, however, came with the advent of the fluorescent bulb. It relies on an entirely different process called arc discharge, in which an electrical arc travels between filaments at both ends of a tube and interacts with gases and a minute amount of mercury to create ultraviolet radiation. When the radiation hits the phosphorescent coating on the inside of the bulb, those phosphors start to glow, Goldmacher said.
Eventually, someone took a fluorescent tube and twisted it to fit in the space of a standard incandescent bulb. The compact fluorescent bulb was born.
Those early compact fluorescents were intended for industrial and commercial use, so no one paid much heed to aesthetics, Goldmacher said. Consequently, the bulbs cast that bluish office light that tends to make people look like they've eaten bad sushi -- a result of the type of phosphors used in the bulb's coating. Better manufacturers, however, have since started using different phosphors to produce a warmer, yellower light that's closer to that of standard incandescents, he said.
The big benefits of compact fluorescents are their longevity and energy-efficiency. Because fluorescent bulbs create light by means of a chemical reaction, very little heat is generated, Rey-Barreau said. That means most of the energy goes into making light -- as much as four times the light per watt of electricity used as that produced by standard incandescent bulbs.
Think of a light bulb like a car, Goldmacher suggested. But instead of measuring in miles per gallon, the efficiency of a light bulb is measured in lumens per watt. A lumen measures the amount of light produced; a watt, the amount electricity used.
A standard incandescent bulb might produce eight to 15 lumens per watt; a halogen, up to 25 lumens per watt; and a compact fluorescent, up to 70 lumens per watt. If the standard incandescent is the Hummer of the light bulb world, the compact fluorescent is the Prius.
What's more, a compact fluorescent bulb will last about 10,000 hours -- say, five to eight years of typical use -- compared with 750 to 1,000 hours (around three to six months) for a standard incandescent and 1,500 to 3,000 hours for a halogen. So that Prius will still be on the road years after the Hummer has been retired to the junkyard.
LED leads way
Rey-Barreau said manufacturers are starting to produce LEDs for household lighting use, and their longevity will far outstrip even that of compact fluorescents.
An LED, or light-emitting diode, works by means of a semiconductor chip through which electrons move to create energy and emit light. Most of us are familiar with the use of LEDs to light digital clocks and cell-phone screens, but manufacturers are combining a number of tiny LED bulbs to produce brighter lighting sources such as brake lights, traffic signals and now household light bulbs.
Know your needs
OK, those are the basic types of bulbs, but why are there so many variations lining the shelves?
For the most part, the differences are largely a matter of size and shape. Some bulbs are shorter so as not to extend beyond the shade (think, for example, of those stubby glass shades on ceiling fan lights). Some, such as floodlights, are shaped to cast a wider light beam. Others are round or flame-shaped so they'll look more attractive in fixtures where they're visible.
A few, however, have special functions. Shatterproof bulbs, for example, are designed with safety in mind. Rough-service bulbs stand up better to vibration and abuse. Full-spectrum bulbs create a light closer to sunlight, which some people believe elevates their mood.
The key to choosing, then, is thinking about where you're using the bulb and what you want to achieve. ``You have to decide what's important for that particular application,'' Goldmacher said, be it energy efficiency, ambience, long life or other reasons.
Then that seemingly overwhelming selection suddenly becomes a little more manageable.
Even for those of us who aren't exactly Edisons.