Since their introduction nearly 30 years ago, compact fluorescent lamps (CFLs) have made slow but sure progress in replacing incandescent tungsten light bulbs, which are essentially unchanged since Edison started selling them in 1879. Incandescents will soon be the dinosaurs of the lighting industry because they're so inefficient, losing 98 percent of their energy input as heat. An incandescent bulb puts out about 17 lumens/watt (a lumen is about the brightness of a candle flame), while a CFL is about four times as efficient, roughly 50-60 lumens/watt. In addition, the average lifetime for a CFL is about 8,000 hours, five times that of an incandescent bulb.
Lighting now accounts for about 10 percent of household electricity use in this country, so a switch to CFLs could save as much as 7 percent of total household usage, a huge step toward a nation's energy conservation. Recognizing this, the European Union has begun the process of scrapping incandescents, while the U.S. will be phasing them out, starting with 100-watt bulbs, in 2012.
Meanwhile, another replacement for incandescent bulbs is just beginning to make a dent in the market. LEDs (Light Emitting Diodes) are twice as efficient as CFLs, delivering up to 112 lumens per watt. With anticipated lifetimes of 30,000 to 50,000 hours, LEDs look like the light of the future. They don't contain mercury (unlike CFLs), they don't flicker, they barely dim with age, and some models are now dimmable (again, unlike CFLs). Light output from LEDs is also directable, minimizing loss of light to the surrounding fixture and ceiling.
The bugbear is cost. A 60-watt equivalent LED will set you back $20-$60. Taking into account both the savings in electricity and cost of replacement bulbs, this still might make sense, even when stacked up against CFLs -- especially in hard-to-reach locations like high ceilings. However, research is proceeding apace. Two years ago, Cambridge University researchers reported developing a $3 LED bulb, 12 times as efficient as an incandescent bulb, with an anticipated lifetime of 100,000 hours. All in all, the future of LEDs looks (wait for it) very bright.
Barry Evans (firstname.lastname@example.org) would like to see all street lights replaced with downward-facing LEDs, the better to see stars at night.
In the photo: Two 7-watt "GeoBulbs" from the Fortuna company, C. Crane (ccrane.com). The bulb on the left has a conventional warm color (2600 degrees Kelvin), similar to an incandescent 40-watt bulb. On the right, a more efficient 5000 degrees K bulb, equivalent to a 60 watt incandescent bulb (taking directionality into account). In the center, a single LED. Each bulb contains eight such LEDs. Photo by Barry Evans