How long is a piece of string? When talking about how long an LED lamp will last, that certainly seems to be the state of the question.
Manufacturers of LED lamps, which many regard as the next generation of lighting, destined to eventually replace today’s incandescent and compact fluorescent lighting sources, make wild claims as to product life.
Typical incandescent bulbs last 1,000 to 2,000 hours. But in speaking about LED replacements, lamp life is routinely quoted as 25,000 to 50,000 hours. Long lamp life, and the reduced power used to create the same amount of light, is what makes this technology so promising.
But what does a 25,000-hour life mean? As it turns out, no one is quite sure yet. The definitions surrounding LED lamps, a nascent technology, are still being made up as we go along.
One thing we do know: It means something different than when people think about the life of a regular light bulb.
When it’s said that a standard light bulb will last 1,000 hours, that is the mean time to failure: half the bulbs will fail by that point. And because lamp manufacturing has become so routine, most of the rest will fail within 100 hours or so of that point.
But LED lamps don’t “burn out.” Rather, like old generals, they just fade away.
When a manufacturer says that an LED lamp will last 25,000 or 50,000 hours, what the company actually means is that at that point, the light emanating from that product will be at 70 percent the level it was when new.
Why 70 percent? Turns out, it’s fairly arbitrary. Lighting industry engineers believe that at that point, most people can sense that the brightness isn’t what it was when the product was new. So they decided to make that the standard.
Of course, brightness is subject to the old frog in the boiling water syndrome. I’m sure that most people won’t even notice the lower level then, if they’ve lived with the same bulb for its entire life. (How many owners of rear projection DLP TVs only realize that a TV’s image has dimmed once they replace the bulb?)
If nothing else in the lamp fails, like its electronics, the product will continue to work until it becomes really dim. But some engineers are proposing a way to get around even that.
Their idea is that once the LEDs start to emit less light, increase the power to each one to increase its brightness. Unfortunately, that will also diminish the life of the lamp.
Good idea, or bad? “The utilities really don’t like this idea,” Fred Welsh, a Department of Energy consultant, told me on Thursday at a lighting conference sponsored by his federal agency.
Not only would contractors need to use thicker cables, but the utilities would need to create more power, partially negating the appeal of LED lighting in the first place.
But still, it’s in its early days, and no one yet knows how this will be settled, or how the consumer will be educated to think about “bulb life” in a different way than they have for the past 130 years. If consumers are going to switch to this new lighting technology, it’s an issue that needs to be settled.
And if it isn’t? “This is a potential black eye for the industry,” Mr. Welsh said.
