I just recieved a cool little LED keychain light. It’s about the same size of the top joint of your thumb, though only about as thick as 3 stacked coins. This thing is amazingly bright for its size. Powered by one ‘coin’ type battery it puts out about half the light of my penlight Mag-lite, which I think is pretty impressive by itself. However the manufacturers claim this thing will run for 100,000 hours on this one battery. That’s about 11 years. Now I’ll grant that the light production may drop off over time, but even so, producing visible light for 1 years non-stop on one battery would be impressive to me.
Now I’ve seen plenty of LEDs before, but the battery powered ones usually put out about enough light to enable you to see them and that’s it, using them as a flashlight is impossible. The bright ones always seem seemed to be power by AC or massive batteries like those programmable roadsigns (which I assume are LEDs).
So the questions:
Can someone give me a basic rundown on how an LED actually works.
2)How does anything produce this amount of light for that period of time on such a tiny energy source?
3)When did LEDs get so bright? Is it a new invention? If not why haven’t I ever seen these things before?
Are you sure the battery life is 100,000 hours?
I thought the battery life of such an LED is geerally around 100 hours.
I suspect you will find that 100,000 hours is the life of the LED itself.
-Oli
The package said 100, 000 hours without battery replacement. I kind of assumed that it relies on the light getting considerably dimmer as the battery dies.
Even if it’s only 100 hours however that is still a long way ahead of a penlight torch which runs on a couple of dry cells and will only last 10 hours.
You may be right, it is just that I have a LED headlamp that is powered by 3 AA batteries, and it states battery life as 100 hrs and LED life as 100,000 hours. Not related to your question, but I believe certain types of LEDs (OLEDs) are currently being adapted for use in computer monitors.
-Oli
Well, you always could test it…coin batteries aren’t too expensive. Just leave it on for a few days and see what happens.
I have a few of those lights and love 'em. I haven’t replaced the batteries in any of them yet, and I’ve been using them for a few years now. In fact, if memory serves me correctly, mine have 2 of those batteries in them.
I wonder if the claim means that with normal usage, the battery doesn’t need to be changed for 11 years (roughly 100,000 hours). I seriously doubt there is anything that energy efficient in existence today. Think about what those coin batteries are normally used for- watches. I think a digital watch would use less energy than an LED (simple watch, no light, alarm, etc.) and I would expect to replace that battery every 4 to 5 years since it is running 24/7…
I don’t know if I can explain this in plain english, but basically an LED is a certain type of semiconductor thingy called a diode. Diodes let electricity pass in one direction and block it in another direction. There is P type semiconductor and N type semiconductor, and if you grow (yes grow, it’s a crystal) P type semiconductor then grow N type semiconductor on top of it you have a diode. If you then grow another P type layer on top of that you create a transistor, but that’s a whole other discussion. Basically, to create P and N type semiconductors you start with a certain type of material like silicon or gallium then add impurities to it to make either P or N type semiconductors (like boron or aluminum for P type semiconductors or phosphorus or arsenic for N type semiconductors).
Anyway, as electrons move across the junction between the P and N type material they give off energy in specific wavelengths of light. For example, a gallium-arsenide diode will give off infrared light, which is useful for things like your TV remote control. A gallium phosphide diode will give off a green light.
LEDs are fairly efficient little buggers compared to filiment type lights.
The manufacturing techniques for LEDs have improved fairly dramatically in recent years. We’re now seeing big bright LEDs and also white LEDs, and at reasonable prices now too. It wasn’t that long ago that blue ones were very pricy and you couldn’t even get white ones.
I suspect that you’ve got it wrong – 100,000 hours is the typical lifetime of an LED. Batteries stop working well before then. And LEDs don’t “run down”, so you can’t count on a lower drain to keep your battery going longer. I suspect either you misread the package, or they mis-wrote it.
Supplemetantary question. If “as electrons move across the junction between the P and N type material they give off energy in specific wavelengths of light”, how exactly do we get white LEDs?
A white LED is a blue LED with some phosphorous added. The phosphorous absorbs some of the blue light and re-emits it in lower frequencies. It’s still mostly blue light coming out, but our eyes see it as white.
In a conventional light bulb, the energy goes into heating up your tungsten filament, which gives off light that is a pretty good approximation of blackbody radiation (the emissivity of tungsten isn’t 1, but it gets closer to it the hotter it gets). Most of the photons emitted are in the infrared, where they don’t do you much good in seeing, but they do a bang-up job of making things hot.
In an LED, most of the energy goes directly into visible photons, all of which you can see. Some energy is lost to phonons (vibrational quanta), which just go top heat things uip, but it’s a much, much smaller proportion than what goes into IR photons in a tungsten bulb. So LEDs don’t get very hot, and they’re very efficient.
Tungsten bulbs “burn out” because of thermionic emission. Hot metal naturally loses surface atoms to ionization. They end up splattered on the inner surface of the bulb. This is why bulbs turn dark. Eventually the filament loses so much metal that it breaks. You can slow down the process by adding noble gas to the interior of the bulb. This causes the ions to re-attach to the filmant, lengthing the bulb life. Ironically, this works best if the bulb is running hot – that is, inefficiently. To tell the truth, I don’t know what the failure mechanism is in LEDs, but it’s not thermionic emission, so these can have lifetimes of 100,000 hours (the typical figure given by manufacturers) or more.
I heard UV LEDs have finally been developed. I wonder if they will now be used (instead of blue LEDs) for exciting the phosphorous in “white” LEDs? I would think so, since (I believe) florescent bulbs use UV…
I bought one of those LED lights, and also thought it said the batteries would last 100,000 hours. However, if you read it carefully, it doesn’t exactly say that. I think it is intentionally vague, but it appears to be talking about the life of the LED.
