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LED Light Emitters: Failure Mode?

Discussion in 'Electronic Repair' started by (PeteCresswell), Jan 19, 2008.

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  1. Do LED lights fail completely or gradually?

    i.e are they all-or-nothing?

    I've got a nice little LED flashlight that, one day, started
    getting dim.

    Noticed that some of the contacts were corroded and wire-brushed
    the ones on the back of the emitter module. The plate that
    connects the two stacks of AA batteries in the back recess of the
    light's body is inaccessible so, after scratching it a little
    with a long knife to no avail, I folded up some alu foil and
    stuffed it down there... but still no luck.

    Fooled around with it today, and couldn't even get a dim light by
    applying 6v from a known good source to the feet of the emitter

    My first thought was that I'd hosed the LED completely by
    accidentally applying reverse polarity somewhere along the line.

    If not, what about the gradual dimming? Does that fit with LED
    failure, or does it narrow the cause down to some sort of
    electrical contact issue?
  2. Meat Plow

    Meat Plow Guest

    An LED can grow dim if the input voltage is too high but I've never heard
    of one gradually dimming. This does not mean that it doesn't happen of
  3. Ron(UK)

    Ron(UK) Guest

    I have several of those little led keyring torches, and they do grow
    dimmer after a time compared with new ones even with brand new batteries.

  4. Meat Plow

    Meat Plow Guest

    Cheap Bastards, how dare they!
  5. mc

    mc Guest

    Gradual dimming is the normal way LEDs wear out. I thought it took years,
  6. Keith G

    Keith G Guest

    OK, Meat Wanka - we're in your parlour now. Let's see what Mr Big Mouth
    Show-Off's like when he's at home....

    (I'll be in touch soon, sweedie.... ;-)
  7. If you overdrive them it will happen much faster. I've done that a few times
    playing with LEDs.

  8. **White LEDs wear out pretty quickly. They are a blue LED with a fluorescent
    coating. The coating fails. Regular coloured LEDs can last for many decades,
    whilst I've found white LEDs will dim to around 30% of their original output
    after about 1 - 2 years of continuous duty (at rated current). Higher
    currents will accelerate that wear.

    Trevor Wilson
  9. Andy Cuffe

    Andy Cuffe Guest

    I have some blue Philips LED christmas lights that I was using as a
    night light. After they were on 24/7 for a year a number of LEDs had
    failed short circuit and the rest were 50-75% dimmer than new. I was
    very disappointed with them. Ordinary light bulbs last longer than
    that! They were either using cheap LEDs, or over driving them (or
    both). Looking directly into the dim LEDs I could see large dark
    areas on the dice.
    Andy Cuffe

  10. Arfa Daily

    Arfa Daily Guest

    I believe that some of these LED flashlights use drive electronics built
    into the head, to pulse the LEDs rather than DC drive them. It apparently
    produces a greater light density per amp, and helps to prolongue the life of
    the LEDs. It's possible that the one that has failed may have such
    electronics, and that's where the problem lies ??

  11. Don't do that! You'll put your eye out!
  12. Maybe _that_ explains the "large dark areas ...."
  13. **Certainly possible. However, it depends on the electronics driving the
    LED. Manufacturers have a tendency to drive the LED as hard as possible, in
    order to obtain maximum brightness. They don't care if the thing fails in
    six months. The money is already in the bank.

    Trevor Wilson
  14. Meat Plow

    Meat Plow Guest

  15. Keith G

    Keith G Guest


    Meat Wanka's tired - must be past his bedtime! (Perhaps he should try
    wearing boxing gloves at night - then he'd not be so *beat up* during the
    day! :)

    At least his tits aren't still slapping the keyboard....
  16. James Sweet

    James Sweet Guest

    It depends on the LED, some of them do in fact grow dim, the blue LEDs on my
    PC used to be identical, now the hard drive LED is considerably brighter
    than the power LED which is on far more. The phosphor coated LEDs dim even
    faster, white and pink LEDs are a phosphor over a blue chip.

    I've had some too that got dim and flickered. I don't know the exact
    mechanism of failure.
  17. James Sweet

    James Sweet Guest

    I have some too that have bad LEDs, they flickered horribly as well, one set
    I modified with a rectifier and it was MUCH nicer looking then, it lasted a
    couple years but now has one dim flickering LED. My friend gave me some more
    sets which had not been modified and they have several more bad LEDs so it
    isn't the rectifier that did it. I'm not impressed with LED Christmas
    lights, they're just not there yet.
  18. What you're saying suggests that the LEDs are simply connected across the
    power line in series, with the LEDs serving as their own rectifiers, so to
    speak. Glitches and spikes in the "reverse" direction aren't going to do the
    LEDs any good. Adding a rectifier presumably provides protection.
  19. Jimmie D

    Jimmie D Guest

    They probably were being overdriven. I have some blue LEDs that are on 24/7
    now for 3 years without any sign of dimming. 2 of then make an excelent
    bathroom night light. I reccomend using a small transformer to step the
    voltage down to something close to the value they need. The LEDS will still
    have to draw there rated current if you use a resistor to drop the voltage
    from 120 you might as well use a light bulb instead of an LED.
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