Supbeam Light
Results 1 to 7 of 7

Thread: Do LED bubls weaken/lose brightness over time?

  1. #1
    Flashaholic
    Join Date
    Aug 2006
    Location
    San Antonio, TX
    Posts
    100

    Default Do LED bubls weaken/lose brightness over time?

    I was wondering if LED's slowly dull after hours of use, or do they just quit at the end of their 100,000 hour or 50,000 hour life?

  2. #2
    Thread Killer Illum's Avatar
    Join Date
    Apr 2006
    Location
    Central Florida, USA
    Posts
    12,447

    Default Re: Do LED bubls weaken/lose brightness over time?

    Welcome to CPF!


    theres a couple of threads open to this topic, LEDs will lose their brightness over time, but that amount of time before a significant drop in output is nearly impossible for any user to attain under normal operating conditions...

    try this thread: http://candlepowerforums.com/vb/showthread.php?t=131304

  3. #3
    Flashaholic
    Join Date
    Aug 2006
    Location
    San Antonio, TX
    Posts
    100

    Default Re: Do LED bubls weaken/lose brightness over time?

    Thanks I tried a search, but since the title is a litte different than what i was looking for, it came out a little spotty. Thanks for the welcome

  4. #4
    Flashaholic*
    Join Date
    Apr 2002
    Location
    Boise, ID
    Posts
    2,639

    Default Re: Do LED bubls weaken/lose brightness over time?

    LED lifespan is rated to a percentage of the initial brightness. Most LED lifespan estimates are to 70% of initial brightness. Luxeon LEDs will get slightly brighten over the first few thousand hours. The brightness dropoff is very gradual at first, then steepens near the end of the LEDs life. LEDs don't simply blink off unless there is a major failure due to a power supply problem (such as being severly overdriven or severly overheating).

    5mm LEDs are shown to not get anywhere near their rated lifespan, due to a poor thermal path from the LED chip, and the clear epoxy encapsulent yellowing/fogging over time. This is especially true of blue and white LEDs, where the blue light significantly acellerates the degridation.

    Luxeon LEDs will actually achieve their rated lifespan if properly heatsinked and driven with a proper current regulator. They have a very good thermal path from the LED chip to a heat sink attachment point, use a silicone encapsulant to ease bond wire stress, and an acrylic dome to prevent yellowing/fogging.

    Read this document from lumileds, it shows the effects of heat and drive current on several types of luxeon LEDs, and is using actual test data:

    http://www.luxeon.com/pdfs/RD25.pdf

  5. #5
    Flashaholic*
    Join Date
    Dec 2002
    Location
    Tennessee., USA
    Posts
    1,535

    Default Re: Do LED bubls weaken/lose brightness over time?

    My Streamlight 4AA7LED was replaced (by SL) because a couple of the LEDs began strobing.

    This was the second version, still seriousy overdriven.

    The new module was easily three times as bright as the old.

    Serious degradation here. I think I ran 3 sets of batteries through the old one, so maybe 12-15 hours of operation.

  6. #6
    Flashaholic
    Join Date
    Apr 2006
    Location
    Virginia
    Posts
    286

    Default Re: Do LED bubls weaken/lose brightness over time?

    Quote Originally Posted by evan9162
    Well constructed technical documents bring a tear of joy to mine eye.

    Now if we can only get everybody to evaluate lights in such a manner


  7. #7
    *Retired* NewBie's Avatar
    Join Date
    Feb 2004
    Location
    Oregon- United States of America
    Posts
    4,946

    Default Re: Do LED bubls weaken/lose brightness over time?

    The small 5mm LEDs degrade really fast, especially if they are overdriven.

    Good examples:
    http://www.candlepowerforums.com/vb/...d.php?t=126857

    A actual product that degrades really fast:
    http://www.candlepowerforums.com/vb/....php?p=1583347


    There are the LEDs that were designed as higher power parts from the get go, made by Philips (Luxeon), Nichia, SSC, CREE, OSRAM (used to be Siemens), and others. You will notice their construction is quite different, designed to greatly lower the thermal resistances (so you can get the heat out), and using larger die, to handle the power better, as well as using silicone instead of epoxy/acryllic to greatly reduce the effects of yellowing with the high lighting and heat levels. You will notice they also have robust thermal interfaces to allow you to heatsink the parts properly. There are a number of other things, but these are the nuts and bolts.

    Each company has a number of application guidelines, which are designed to allow you to properly employ these high power parts, and maintain the performance of the devices over time, and they should be closely followed and understood.

    As an example, OSRAM has specific information for dealing with just the thermal requirements:
    http://catalog.osram-os.com/media/_e...00036578_0.pdf

    And the electrical requirements:
    http://catalog.osram-os.com/media/_e...00015957_0.pdf

    Other things available are stuff such as reliability information (check out the g forces these can take):
    http://www.cree.com/products/pdf/XLamp_Reliability.PDF

    CREE has their thermal guidelines also:
    http://www.cree.com/products/pdf/XLa...Management.pdf

    Philips has their guidelines as well, for their Luxeon devices:
    Electrical:
    http://www.lumileds.com/pdfs/AB11.PDF
    Lifetime:
    http://www.lumileds.com/pdfs/AB07.PDF
    Thermal:
    http://www.lumileds.com/pdfs/AB05.pdf

    Seoul Semiconductor Corporation:
    Reliability:
    http://www.essc.co.kr/_HOMEPAGE/home...eliability.pdf
    Thermal Management:
    http://www.essc.co.kr/_HOMEPAGE/home...ec/thermal.pdf
    Electrical:
    http://www.essc.co.kr/_HOMEPAGE/home...electrical.pdf
    Electrical failure modes:
    http://www.essc.co.kr/_HOMEPAGE/home...ailuremode.pdf


    LED myths:
    http://www.lumileds.com/pdfs/10Myths1.PDF
    Last edited by NewBie; 09-07-2006 at 09:59 PM. Reason: add more comments

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •