[hairytoes]

Autumn is here, which means commuting in the dark again.

I loved my front light last year, it seem adequate (Luxeon K2 driven by 1A buckpuck).

Just started using it again, and it seems dim. I don't have anyway of measuring the output.

Is it possible that the LED is just wearing out and decreasing output? Runtime has probably been about 250-350 hours.

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[ericy]

Autumn is here, which means commuting in the dark again.

I loved my front light last year, it seem adequate (Luxeon K2 driven by 1A buckpuck).

Just started using it again, and it seems dim. I don't have anyway of measuring the output.

Is it possible that the LED is just wearing out and decreasing output? Runtime has probably been about 250-350 hours.

No, LEDs don't wear out. I would look at the batteries first.

[hairytoes]

'taint the batteries - the power is supplied via a buckpuck, so provides a constant current regardless of battery state (right up until they go dead flat).

[kf5nd]

hairytoes, it's most probably a bad cell within your battery pack. The cell has gone bad (short-circuit), and is now contributing zero volts. LEDs do not wear out over a one year time scale.

This is why I use consumer rechargeable cells. If one goes bad, I just pitch it, and then I complain to the manufacturer and get a $5 off coupon for some new ones. Keep your receipts.

[HandsomeRyan]

as mentioned, unless you overdrive them and turn them into smoke emitting diodes, LED's have a lifespan of 100,000+ hours. That's a little over 11 years of constant illumination.

[n4zou]

hairytoes, it's most probably a bad cell within your battery pack. The cell has gone bad (short-circuit), and is now contributing zero volts. LEDs do not wear out over a one year time scale.

This is why I use consumer rechargeable cells. If one goes bad, I just pitch it, and then I complain to the manufacturer and get a $5 off coupon for some new ones. Keep your receipts.
He is running an LED driver circuit. Even if he had a shorted cell the LED should be producing the same amount of light. The run time of the batteries would be much reduced by a bad cell, not light output. I would open it up and check for crud or cold solder joints around the LED and driver circuit. It is possible the driver circuit is going bad as well. If you could put an Amp meter between the driver board and LED that would show any reduction of current feeding the LED.

[CameraMan]

If you've been running it at 1A without a sufficient heatsink - that would certainly explain your early death syndrome.

http://www.lumileds.com/pdfs/WP12.pdf

[hairytoes]

It's mounted directly onto a 1" cube heatsink, but is getting warm. Not hot, but warm

I wondered about corroded joints. I'll take my multimeter up with me when I'm doing some bike repairs, and check that.

[edzo]

No, LEDs don't wear out. I would look at the batteries first.


incorrect.

led's do wear out. just not much

the initial degradation in the first few hundred hours is the greatest,
then they settle and wear out at a much lower rate.

however, the percentage of degradation is quite small and should not be
noticeable without a sensitive meter...

except on cheap, poorly made leds, or leds which are improperly driven or heatsunk

[CameraMan]

It's mounted directly onto a 1" cube heatsink, but is getting warm. Not hot, but warm

The heatsink should be getting too hot too hold i.e. >50 deg C, without airflow.
Is the thermal compound between the LED-Substrate-Heatsink okay ?

However this could also point to a lack of current I wondered about corroded joints

[hairytoes]

It doesn't get that warm - but then there is always airflow, as the heatsink is bare, screwed directly to a handlebar mount.

The K2 led is rated at 1.5A, and I'm driving it at 1A, for longevity.