I’ve been intrigued by some things I’ve read about the advantages of LED lights, and even seen some websites selling the bulbs for easy replacement in household fixtures. I would love to replace the bulbs in a couple of difficult ceiling lamps, as well as get a great deal more brightness out of a bathroom fixture.
What I wonder is, are the bulbs as reliable as is claimed (suggestions I’ve read are that they could easily last 5 years, and as much as 10). and how can you get a handle on how bright they are compared to standard household bulbs (I can find no easy comparison between, say, a 60 watt lamp bulb and an LED replacement)?
I’d also be curious if anyone has actually tried it, and what they felt the quality of the lighting is like. Is it a good, clear white light, or uncomfortalby harsh?
This is more of a bump than a full answer - I’ve not had experience of white LEDs designed to replace mains lamps
A manufacturer?s web site should give you their *estimated * life for a particular product - LEDs do generally have long lives, however white LEDs have a tendency to change their colour as they age.
LEDs aren’t actually that efficient (yet) - IIRC their output per watt is roughly the same as a halogen lamp, i.e. better than a plain vanilla bulb, but way less than “Lo-energy” fluro bulb.
AFAIK all “white” LEDs (rather than the “effect” ones that can be varied to any colour) are actually blue LEDs with a fluorescent layer to convert most of the blue to other colours - so the light quality is similar to a “Lo-energy” fluro bulb rather than like a standard incandescent light
So, prob not many advantages over a “Lo-energy” light, same nasty light quality, less efficient (so run hotter), may well last longer, can be turned on and off as often as you like without blackening and no delayed turn on.
There’s also a cleverly doped LED material that simultaneously puts out R, G, and B. It was written up a couple years ago (sorry, can’t find cite), but I don’t think it’s made it into commercial applications yet.
But, again, the article goes on to point out the problems with replacing white light sources with LEDs right now. I would point out, though, that even small white LED flashlights are astonishingly bright and the batteries seem to last forever - so I’d expect the barrier to household use will fall over the next few years.
I haven’t tried an LED-based replacement for a traditional light bulb myself, but all the reviews and reports I’ve seen say that they are very disappointing. They are very dim - no where near as bright as claimed - and they have the lousy color rendition that most white LEDs are stuck with. Whatever the truth of those claims, there is no denying that they are also appallingly expensive.
Compact fluorescents, on the other hand, have made serious strides in the past 3-5 years. They’re far more efficient than LEDs and incandescent bulbs. I have several of these at home, and they’re pretty reasonable alternatives for incandescent lamps in most places.
I looked into LED lighting (and destroyed $12 in white LEDs while experimenting), but now mini-flourescents are starting to appear in dollar stores, and dimmable flourescent bulbs are appearing in hardware stores. By summertime, I’ll replace the 300W halogen in my office (in the winter months, it makes for a handy heater, but it’s hell in summer) with a ceiling fan equipped with three 24-watt flourescents, each the rough equivalent of a 100-watt incandescent. LED light bulbs exist, but I’ll get by with flourescents for a few years until LEDs improve and quality and drop dramatically in price.
It’s true that LEDs are great for traffic signals and flashlights, but they both turn out to be fairly special cases.
In the case of traffic signals, LEDs have two efficiency advantages. First, colored LEDs - particularly red and green LEDs - are much more efficient than white LEDs or incandescent bulbs. Second, they don’t need a colored filter, which absorbs most of the bulb’s output in a traditional traffic signal. As a result, an incandescent signal that consumes something like 600 watts of power can be replaced with an LED system that uses about 40 watts. Consider that a traffic light runs 24/7 and you can see how the electricity savings pile up fast. An additional benefit is long life - the LEDs will probably last 50,000 to 100,000 hours, compared to 5,000 to 10,000 for incandescent lights. So there is a savings on labor for bulb changes, too.
In the case of flashlights, LEDs have different advantages. Most importantly, LEDs are a lot tougher than light bulbs - there is no filament to break, so there’s less chance you’ll suddenly be left in the dark when you need the light most (like when you’ve just fallen off a ladder, say). Secondly, although LEDs are not significantly more efficient than incandescent bulbs, their efficiency also doesn’t plummet as the batteries get weak. With an incandescent flashlight, by the time the batteries are down to about 70% of their original voltage, the bulb can only produce about 30% of the original light. Most LED flashlights will get dimmer as the batteries die, but don’t experience the horrific efficiency dropoff that ordinary flashlights do. Batteries that can barely light an incandescent bulb can still produce useful output in an LED flashlight.
So I’m afraid the advantages LEDs are currently exploiting in traffic signals and flashlights don’t really apply to general-purpose indoor lighting. If LEDs eventually become more efficient than fluorescent bulbs, though, they may make serious inroads.
Anyone interested in flashlights, LEDs and/or LED flashlights might want to check out the Candlepower Forums.
Yesterday on NPR I heard that the Japanese scientist that perfected the blue LED (and had something to do with blue lasers as well) just won a settlement against the company he used to work for. To the tune of $200 million.
Lately I have been experimenting with LED flashlights, as a matter of trying to find a way to make a cheap IR flashlight to use with night-vision goggles.
A couple things I’d point out is that first of all, LED’s seem to produce a lot of light, but most of the light they give of is straight out the front of the LED itself–they do not radiate in 360-degrees the same way that bulbs do. So looking with a LED pointed “straight at you”, they certainly seem very bright–but if you place a LED into a regular flashlight reflector (as I have done, http://www.norcom2000.com/users/dcimper/assorted/whatever/led_lite.html ), you see that they simply do not produce nearly as much light as even a small incandescent bulb would. Most of what they produce runs out the front end of the LED in a 30-degree or so cone–so it doesn’t work real well to just “replace a bulb with a LED” yourself, you need a different reflector as well to distribute the light well. -Or you would use special LED packages, as mentioned further below.
The second matter is that it’s very electrically efficient to run a LED at constant low-voltage and current–and that gives LED’s their long lives–but that’s not how white and other “high-brightness” LED’s work. They use pulsing circuits that alternate a signal that is far above their rated voltages, but they cool down between pulses, so they keep working. The question about this is–how long they will keep working this way. As it is, LED’s are all assumed to have a “10-year” lifetime and so LED fixtures generally aren’t made to allow easy replacement of the LED’s–but if these things are driven hard they may not last their usual rated lifetimes. Probably the best examples of this are the high-priced $100+ “tactical flashlights” sold–they use one or two 3-volt Lithium batteries and they run their bulbs and LED’s extremely bright, but they often don’t run for more than an hour before the batteries are discharged. RUn in constant-voltage fashion, those batteries should light those LED’s for at least 4-5 days, so you’re getting 4-5 days of “LED wear” in an hour.
About the brightest visible LEDs I can find right off now is the “Luxeon Star” ones. A flashlight replacement bulb is sold online for about $40. I don’t have one, but from the photos of it you can see it uses a special odd-shaped package to try to distribute its light more evenly, and it has pulsing circuitry built-in.
No, they are driven by pulses of high current. The voltage drop across an LED is more or less constant once the LED turns on fully. The pulses are arranged so the average current remains below the rated I[sub]Max[/sub] of the LED, but the peak current can greatly exceed this. Some math and stuff here, for those interested.