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View Full Version : Do L.E.D.s dim with age?



Frosty
05-19-2005, 22:29
I couldn't find my headlamp while packing for a weekend trip so I went to Wal-Mart and bought another. Same kind as my old one (the $12.77 kind).

It came with batteries and the light seemed very bright.

Before I could pack my new light, I found my old one. It wasn't nearly as bright as my new one. One might assume that the old one needed batteries, but I'm an engineer and I jsut can't help myself sometimes.

I put the new batteries in the old light, and the old batteries in the new light. SURPRISE! Even with the old batteries, the new light was still brighter, though not by quite as much.

Both headlamps look identical, and I doubt much re-engineering goes into a twelve dollar item.

Now I am faced with four possibilities:

1. L.E.D.s grow dim with age
2. L.E.D.s grow dim with use
3. My old light was a production anomaly, and is not as bright as other units
4. My new light is a production anomaly, and is brighter than other units

The last two I tend to discard because of the great difference in brightness. Headlamps are merely LEDs connected to batteries with a switch. The only real variable are the LEDs themselves and I suspect they do not vary that much in production.

Intuitively, I lean toward No. 1, but have no data to back this up.

Anybody know?

Heater
05-19-2005, 22:44
Now I am faced with four possibilities:

1. L.E.D.s grow dim with age
2. L.E.D.s grow dim with use
3. My old light was a production anomaly, and is not as bright as other units
4. My new light is a production anomaly, and is brighter than other units


5. Different LED manufacturer?

Maybe a different manufacturer might make a brighter LED.

Hmmmm.... I wonder who makes these LEDs? :-?

neo
05-19-2005, 22:48
only when your batteries run down:cool: neo

Moon Monster
05-19-2005, 23:42
Yes, LEDs can indeed loose output. Though it takes a long time to become noticeable. The loss is likely due to heat output of the circuit. Perhaps the cheaper headlamps are more prone to this due to poorer engineering/insulation.

Check out this paper:
http://www.lrc.rpi.edu/programs/solidstate/pdf/ProjectingUsefulLife.pdf

LEGS
05-19-2005, 23:44
HEY FROSTY, IF ITS ANY HELP, I BOUGHT A NEW PETZEL TIKA COMPLETE WITH BATTERIES. I USED IT EVERYDAY FOR 2-1/2 MONTHS ON MY HIKE. I NIGHT HIKED ABOUT 35 HRS SINCE IT WAS SUMMER. AND YES THE LIGHTS DID DIM AFTER ABOUT 2 MONTHS, IT WAS NOTICABLE BUT WAS STILL USEABLE, I WANTED TO SEE HOW LONG BEFORE IT WENT OUT COMPLETELY. I CAME HOME AND STILL USED IT AROUND THE HOUSE WHENEVER A FLASHLIGHT WAS NEEDED, THE LED'S GOT DIMMER AFTER ABOUT 6 MONTHS AND I REPLACED THE BATTERIES. THE TIKA WAS A LITTLE BRIGHTER BUT NEVER THE SAME AS WHEN I FIRST STARTED USING IT. THEY ARE GOOD LIGHTS FOR SURE, BUT I BELIEVE THEY DIM WITH AGE AND USE. HOPE THIS ANSWERED YOUR QUESTION, HIKE ON.
I couldn't find my headlamp while packing for a weekend trip so I went to Wal-Mart and bought another. Same kind as my old one (the $12.77 kind).

It came with batteries and the light seemed very bright.

Before I could pack my new light, I found my old one. It wasn't nearly as bright as my new one. One might assume that the old one needed batteries, but I'm an engineer and I jsut can't help myself sometimes.

I put the new batteries in the old light, and the old batteries in the new light. SURPRISE! Even with the old batteries, the new light was still brighter, though not by quite as much.

Both headlamps look identical, and I doubt much re-engineering goes into a twelve dollar item.

Now I am faced with four possibilities:

1. L.E.D.s grow dim with age
2. L.E.D.s grow dim with use
3. My old light was a production anomaly, and is not as bright as other units
4. My new light is a production anomaly, and is brighter than other units

The last two I tend to discard because of the great difference in brightness. Headlamps are merely LEDs connected to batteries with a switch. The only real variable are the LEDs themselves and I suspect they do not vary that much in production.

Intuitively, I lean toward No. 1, but have no data to back this up.

Anybody know?

Frosty
05-19-2005, 23:45
5. Different LED manufacturer?

Maybe a different manufacturer might make a brighter LED.
Hmmm, this I like. New supplier. My "old" headlamp is two years old, so there could have been a change in suppliers.

Anyway, guess I'll just retire my old one.

SGT Rock
05-20-2005, 00:06
Funny, I find mine to be too bright for my taste.

Pencil Pusher
05-20-2005, 01:17
Funny, I find mine to be too bright for my taste.
Is that referring to your .3 oz-wonder? For some reason I am picturing one of those 'key ring' led lights.

Legs, caps lock...;)

Roland
05-20-2005, 04:36
Now I am faced with four possibilities:

1. L.E.D.s grow dim with age
2. L.E.D.s grow dim with use
3. My old light was a production anomaly, and is not as bright as other units
4. My new light is a production anomaly, and is brighter than other units 5. The lens on my old light has yellowed, giving the illusion that its L.E.D.s have grown dim with age
6. My new light was produced using a clearer lens than my old light

SGT Rock
05-20-2005, 08:49
Naw, that is my Zipka Plus. It is brighter than I want, even on the dimmest selection.

hiker5
05-20-2005, 10:00
Rock,

I 've found that using the red lens filter makes the Zipka Plus seem much less intense.

Footslogger
05-20-2005, 10:08
I've got one of the original Petzl Tikka headlights (circa 2000), with a bank of 3 LED's. Recently I switched to the AAA sized lithium cells and as far as I can tell it's as bright, if not brighter, than when it was new.

'Slogger
AT 2003

DebW
05-20-2005, 10:15
Manufacturers are producing brighter and brighter LEDs. Do you have wattage figures on the old and new lamps?

Just Jeff
05-20-2005, 14:22
My Petzl had a graph in the included pamphlet that displayed LED intensity vs hours of use, and it significantly dropped off at one point, but I don't remember what it was...35 hours, maybe? It leveled off at a dimmer intensity but still displayed usability for a long time.

That graph might be on their website, too.

Crazy Larry #1
05-21-2005, 08:17
I've had my Petzl for four years now, having purchased it at Mt Rogers Outfitters and I haven't noticed them dimming yet. In fact I left the same batteries in them for fourteen months while I was cleaning up the wreakage from my past and when I clicked them on, they shone just as bright...........wanderer

DebW
05-21-2005, 14:32
Intensity vs hours of use is a function of battery life. That's based on alkaline batteries - the voltage drops with use and the light intensity will dim. Lithiums have a different voltage drop curve - they will stay near full voltage most of their lifetime, then drop quickly. Light intensity will therefore stay fairly even until the batteries die. The exception to this is headlamps with a voltage regulator, which will give contant intensity light until the batteries die. LED intensity decay is a different issue which I know nothing about.

DLFrost
05-22-2005, 23:16
Manufacturers are producing brighter and brighter LEDs.
They're also producing more lights that are overdriving the LED's for brighter output, now that they have a better understanding of how far you can push em. These will appear whiter/bluer than their within-spec counterparts.

An example: The Pelican L1 lights now advertise a 50k hour lifetime for the LED, which is half the normal lifetime for standard superbright LEDs. The light loads four button cells in rather than the usual one/two for a single LED. Overdrive! I like the tradeoff, actually. You'll loose the thing or get something newer before you use up the regular 100k lifetime. It boasts 100 hours of battery life, which translates into about 30-40 hours of brightest light. (Weighs 1.1 oz. with the "breakaway" lanyard.)

superman
05-22-2005, 23:39
My light stays consistantly bright but I keep dimming.:banana