Dirty LED Secret?!?!

jayflash

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Some of my LED lights have lost aproximatly 10-15% of their brightness from when they were new. Some of them are now consuming 20% more current. The figures are worse for Luxeons than Nichia flashlights.

My BB 400 consumes 650mA from the cells and its output is less than half of original intensity.

Shall I assume the BadBoy problem is just a fluke and my sample of lights is too small and not representative of normal operation? My lights don't have more than 20-25 hours on most of them. Thanks for any input.
 

flashlight

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I heard that overdriving any LED not only dramatically shortens it's lifespan but also brightness eventually. Someone correct me if I'm wrong.
 

The_LED_Museum

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20-25 hours is way too short a time for a typical white or colored LED (except maybe LEDs emitting shorter wavelengths than about 425-435nm, and pink LEDs that use an organic phosphor) to degrade like this.
I think your sample size is too small to say with any measure of certainty if LEDs in flashlights like yours will consistently degrade as you described.

LEDs can degrade faster when overdriven, but I think 20-25 hours is TOO fast.
 

Lux Luthor

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I'm not sure about the BB issue, but heat degrades luxeons - plain and simple. If you want to overdrive them in a flashlight, look for good heatsinking, but also for the ability to easily replace the emitter. I'm still surprised, though, by the 20-25 hour figure. That's seems real low.

edit: Ah, I see Craig beat me to it. /ubbthreads/images/graemlins/smile.gif
 

jayflash

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Yes, Craig, you are (hopefully!!!) probably correct. It may well be that my very limited experience is just a coincidence. Or, I wonder, might LEDs lose a little output after the first few hours and then settle in at a steady output?

My BB 400 must have an atypical problem. Any ideas on that?
 

jayflash

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Thanks, Bushman, I'll do that. I should have emphasized that I was given the light, second hand, and am not upset with the diminished output - it's still a useable light and I run it on NiMH cells, so it was all FREE. /ubbthreads/images/graemlins/thumbsup.gif
 

gadget_lover

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How are you measuring the light loss? Did you do a benchmark test and record the results when you first got them?

jayflash said...
My BB 400 consumes 650mA from the cells and its output is less than half of original intensity.

For the intensity, did you measure the current to the LED, or are you going by visual observation only? 650 ma draw from the battery is not too bad for a sub 3 volt to 3.75volt conversion.

It's been observed that Luxeon Vf may shift as they age. The Vf (as designed) goes up and down with the temperature.

If you lose a significant portion of the brightenss in only 20 hours it would tend to indicate that the heat managemnet is poor or the LED is over driven. 400ma is NOT within spec for a 1 watt luxeon.

Daniel
 

gadget_lover

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If you use NiMh, you have about 2.5 volts for the power supply, so boosting it to the Vf of the Luxeon (typically 3.5 or higher) will account for the 50% higher battery current. If you do the math, 2.5 *.65 (power consumed) is close to 3.5* .4 (power out). That should be an 84% efficient conversion.


There's nothing apparently wrong with your BB assuming that it's putting out close to 400ma.

Daniel
 

jayflash

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Roughly 20 hours, of runtime, ago, the BB consumed about 550mA and now it's up to 650. By meter, it lost about 60% of its original light intensity. The benchmark measurements were all taken several times because I compared performance with three different types of cells. Periodic measurements, since first getting the light, have slowly trended toward the present readings. The BB gets a little warmer than an LSL, both running on NiMH cells, and never felt excessively warm. When running the light for 30 minutes, with the head off and Lux exposed, I never felt the LED get more than warm to the touch.

Are any of those clues useful?
 

Lurker

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I think all of that would be consistent with lower battery voltage on the second test. Could that be a factor?
 
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