LED degration.

LEDs usually have a rated 5000 to 10000 hour life was wondering if the light quality, more for white LEDs, stay the same over all those hours or do they turn green/violet over time?

Huh? I thought most LED's are rated in the 100k hour range. Did I miss something?

5mm LEDs when driven to spec are rated 100,000hrs. The 5W LS is rated 500hrs (or was that 5000hrs?) The 1W is rated 10,000hrs. These numbers are off the top of my head. The main thing is that the phosphor will degrade over time and the rate of degradation increases with raised temperature.

White LEDs are supposed to maintain the original tint such that there is no noticeable colour shift. The only thing that is supposed to happen is a gradual dimming.

BTW, in case you didn't know, those rated life spans are for the LEDs to reach half the original brightness level, not till death.

Steelwoolf,

The 5W LS is rated to 5000hrs.

Doug

anyone here whos been useing an L4 alot? notice any changes in beam color?

I've got some older white LEDs originallyh from Real Goods, that have been running 24/7/365 for around 7 years, and they are definitely showing degradation. These are dimming significantly (I wish I had kept a few unused for "control" samples). They now have a yucky brownish tinge, a couple have failed altogether, but still produce semi-usable "night light" illumination. These are in a series-parallel configuration, three in series with a 100 ohm resistor, powered by a 12VDC wall cube, pretty close to nominal 20 mA current.

I also have some Nichias that have been going over 4 years, they seem to be holding up well. A 36 LED array using some of the white LEDs (manufacturer unknown) from SuperbrightLEDs has been running continuously for 3 years, three of the LEDs are noticeably dimmed down, the rest are still full brightness The are in a an arangement of four groups each in a 3X3 series-parallel with a 100 ohm resistor in series, also feeding from a 12V wart. THis is my bathroom night light.

/ed B in NH

dougmccoy, where did you get your "5000 hrs" figure from?

The latest data sheets on the Lumileds website rate the white 5 watt Luxeon Stars at 500 hours to 75% (@75 C) of the original output.

Peter

[ QUOTE ]
Gransee said:
dougmccoy, where did you get your "5000 hrs" figure from?

The latest data sheets on the Lumileds website rate the white 5 watt Luxeon Stars at 500 hours to 75% (@75 C) of the original output.

Peter

[/ QUOTE ] That makes me tempted to go back to regular bulbs and forget about LEDs. 500 hours isn't long to start with and to find out that 25% of light output will be gone by then. I've noticed many burnt out LEDs when passing 18 wheeler's that have LED brakelight's lately. Maybe LEDs aren't as great as some think. /ubbthreads/images/graemlins/icon23.gif

emann - I agree. LEDs are not perfect. They have lots of failure mechanisms associated with any solid state devices. The 100,000 hour figure was a rather optimistic one even when applied to LEDs without phospher.
ALL lamps have decreasing output with time. Even halogen cycle lamps (very small - a few percent near end of life). These are the best as far as lumen maintainance goes. Fluorescent lamps are not great (20-30% loss) metal halide HID are worse (30% typical) That is why GE specifies INITIAL (at 100 hours) and AVERAGE lumen outputs for their HID and fluorescent lamps. The dimming is very slow so one tend not to notice it until the lamps are replaced!
That said, LEDs are still much better than the incandescent bulb for flashlightlight applications as far as LIFE goes . A typical PR bulb with Krypton gas fill has a rated life of 15-30 hours. Halogen bulbs goes from 20-100 hours. So in this context, even the 500 hours of the 4.8W Luxeons is pretty long. BUT their greatest advantage is their relative mechanical ruggedness. Dropping a properly designed flashlight with LED light source will not damage the lamp. At least, other parts (the battery comes to mind) would have failed first.
You may have gathered that I like LEDs as a light source. But I do accept that they are certainly NOT perfect. /ubbthreads/images/graemlins/grin.gif

You are right, LEDs are not perfect by any stretch. However, I have an SF L4 and a SL TL-3 Xenon. Although the TL3 is much brighter with A LOT more throw, I still prefer the L4 for almost everything which requires the use of a flashlight. /ubbthreads/images/graemlins/grin.gif

I still enjoy seeing the "wall" of white light which the L4 emits.

By the time the L4 starts to noticably loose its ability to put out bright white light, I am sure it will be time to buy an 10 watt luxeon star light. /ubbthreads/images/graemlins/wink.gif