LED lifespan?

I've been learning a lot from this forum, and have just ordered Streamlight, Petzl, Elektrolumens, and Arc lights. Besides the longer battery run time, I was impressed with the longevity of the led emitters.

Now, as I've started thinking of Luxeon-based lights, I read on Lumileds web site that they claim Luxeon led's have better longevity than others. Naively, I had thought the "100,000 hour" ratings of most led's meant they would shine brightly over the full rating. Lumiled seems to say the brightness falls off pretty quickly:

http://www.lumileds.com/newsandevents/releases/June_03_2002_LumMaint_PR.pdf

Is this a concern as we consider longevity of led flashlights that are not using Luxeon star emitters?

Thanks for your help with this question.

I guess it depends on how much you use your lights?

If you use your light, say and hour a day and take that 3000 hour figure, you're looking at 70% brightness after over 8 years of use. If you only use your light an hour a week you're looking at a figure of almost 60 years. If those figures are even reasonably accurate it doesn't seem like too much of a worry to me.

Do keep in mind that many light manufactuerers over-drive their LED for higher brightness (especially the 5mm type) and this will affect the numbers.

Most LED's life spans are rated to 50% brightness. As previously posted this is also based on them being run at their typical spec. and many are run at or over their max. There is also one Luxeon with a rated life of 500 hrs. I'm not aware of anyone using it in production.

Keep in mind other kinds of light sources are rated differently. What follows is from (usually faulty) memory.
Florescent 80% brightness.
Incandescent 50% of the test bulbs have burned out.

The way I've looked at it is to consider the cost of the batteries relative to the flashlight. For instance, let's say you buy a new ARC4 flashlight and the LED degrades to 70% at, say 3000 hours. Come on now, what you had to spend buying batteries to operate a flashlight for that period will make the cost of buying another flashlight seem inconsequential. IMHO, if the LED lasts for a few hundred hours, it's OK for 99% of the users.

Also remember that your eyes operate on a logarithmic scale, not linear.

So a 50% drop in amplitude is really only noticeable if you have two lights to compare side by side (or if you step power between low and high).

While it is nice to always have the most efficient power--the fall off is not going to be very noticeable in real life.

For me, the Arc4 is very interesting concept. You have bright when you really want it--but you can extend your battery life by 2x-8x without serious darkness setting in.

-Bill

Take your 3000 hours and consider this....

If you run it for 2 hours every day you will take about four years to get to the 3000 hour mark.

Given how fast LED technology is improving, don't you think you will wish to upgrade any white LED's you now use in four years time ?

Thanks for the information.

As several of you mentioned, I am beginning to realize that it provides a great reason to explain to my wife why I need to keep upgrading, or better yet, splurging on an ARC 4+ !

I suppose I was just surprised to have my assumptions about LEDs shown to be wrong. Maybe a Luxeon light with several brightness option is the most logical...but I'll have to save up for a while.

Jay

It's a good thing to learn the truth about LEDs. Another common misconception about LEDs is that they're a super-efficient source of light. Not so. In fact a $1.99 Home Depot Fluorescent lamp is more efficient at converting electricity to light.

LEDs do have a number of advantages and, when compared to other small bulbs, like 1-5 Watt incandescent lamps, their efficiency starts to look better.