LED life vs output

I think I have an idea of the answer to this question, but wanted to see what the opinions were on CPF.

LEDs are typically quoted as 100,000 hour life. My understanding of this is that if driven at the quoted current to give the stated output, the output would have dropped to 70% of the original output after 100,000 hours.

OK, so if I have got that right, what can you expect if you run the LED at a much lower output? For example I have a Quark AA and like the moonlight mode. I use this most often especially at night when I don't want to disturb the other half. I would like to leave it on constantly as the clicky switch is surprisingly loud in the middle of the night. I keep it in a bedside drawer and like opening the drawer with a soft glow and then being able to use the Quark without the seemingly loud click.

What I don't want to find is that even at this incredibly low output level that I am counting down the 100,000 hours when most of these are not really used at all, but are just lighting up the inside of a drawer.

So is the life of an LED a function of output time alone, or time AND level, therefore when running in moonlight mode the life may be 2,000,000 hours instead?

Hello Subwoofer,

I believe you do end up with increased life span when you run LED's at lower levels.

However, you may just want to change the way you look at this...

100000 hours is just over 11 years if the light is left on 24 hours a day. If you only turn it on at night, that will more than double the time to 22 years.

In 22 years of constant use, you may find another light that meets your needs and replace it.

Another thing to consider is that LED's don't suddenly shut off, they get dimmer and dimmer.

Tom

subwoofer said:

OK, so if I have got that right, what can you expect if you run the LED at a much lower output? For example I have a Quark AA and like the moonlight mode. I use this most often especially at night when I don't want to disturb the other half. I would like to leave it on constantly as the clicky switch is surprisingly loud in the middle of the night. I keep it in a bedside drawer and like opening the drawer with a soft glow and then being able to use the Quark without the seemingly loud click.

What I don't want to find is that even at this incredibly low output level that I am counting down the 100,000 hours when most of these are not really used at all, but are just lighting up the inside of a drawer.

So is the life of an LED a function of output time alone, or time AND level, therefore when running in moonlight mode the life may be 2,000,000 hours instead?

Click to expand...

That's a valid use regime for the Quark AA. It'll run on Moonlight mode for about 15 days on an alkaline battery. But you have to pay top dollar for a silent clicky. Broadly speaking, there's little tactical value in a silent clicky, so it's not got a large market. I'd suggest you use momentary on with the forward-clicky Quark tailcap, but then the regular sadly ships with a reverse clicky

At even 11 years of service you're likely to be hitting other limits - have you lost the light? Found a better one? Batteries out of style? Capacitors gone bad?

Turning on and off every day, would not be my first choice as the last thing I am likely to remember when crashing is to turn it on. I'm lucky if I remember to set the alarm.

The point about hitting some other limit interests me. Loosing it is not something I would factor in as I am assuming I still have it, but failure of other components is.

So with the driver boards on LED lights, will they last 100,000 hours or will they fail first? The capacitors on the driver board, do they degrade simply with time, or with use? Can we really get 100,000 hours out of an LED if the driver board has any components which might fail first?

With the Quark running in moonlight mode, the driver board must be working quite hard controlling the current. As it will run of either NiMh or Li-ion (which I am currently using) it has to cope with very different voltages so must be relatively sophisticated.

I also wonder about the way the driver manages the battery types. Assuming you can run a NiMh down to 0.6v safely when drawing very little power, what does it do with a Li-ion which has been drained to less than 2.0V, does it keep going until the Li-ion is 0.6v or less?

Also bear in mind that the '100,000 hours' is a quote that may be unrealistic. Just the same as capacity of batteries is often exaggerated, so might be the life of LEDs. Some commentators have suggested that the lifetime might be as low as 2000 hours to 50% on many Asian made LEDs.

However, it is true that the life will be extended if you run them at lower powers, and I would be surprised if moonlight mode did much to use up the available lifetime. Likewise with a driver. The enemy of most electronic components is heat, and they run hotter at higher power loads. So moonlight mode will not be stressful at all.

As for the clicky noise, have you considered a twisty? They are completely silent. For example, I have a mini-Mag with a drop in that turns on and off silently. With a red gel filter over the lens it makes a very good night light.

if an LED is driven at or below spec and heatsinked properly chances are it will outlast the light unless it is a generic cheap junky LED. even 25000 hours used 3 hours a day is over 8000 days or 20+ years. If you are using a light that much in less then 5 years you probably will replace it with a better light way before it is toast and then it will last 50 years or whatever. Those using lights 8 hours a day every day will definately replace them within 5-10 years with a light that has a more efficient emitter and better design. I have a dorcy AAA and it still works but since better lights have come along I rarely ever use it. The majority of the first LED lights I have the usage is less than 1 hour a month now. If you have a headlamp and a keychain light and so on usage is split amongst them such that you won't even get 8 hours a day off any of them.

even at spec these things are getting to 70% or less at more like 20,000-40,000 hours not 100,000. lowly driven leds here have been running for non-stop since they came out. and the phosphors get weak like any phosphor driven thing. less at low or the low spec, but certannly not 100,000 at 70% for any of the phosphor based ones.

ida be really happy to get the 100k and not expect the 2Mill at a low level. everytime i replace one i realise how far gone the phosphors really were.

the 100,000 quote is BS for phosphor based leds, but running it low you might get there .