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I need to make LEDS brighter

Discussion in 'General Electronics' started by Tim Simmons, Feb 8, 2004.

  1. Tim Simmons

    Tim Simmons Guest

    I need to make some hyperbright/superbright LEDs even brighter.

    Under steady state conditions they draw about 20mA at 3.6v. I
    understand that they can be pulsed at a higher voltage for additional
    brightness without reducing their life expectancy. In fact, I have
    heard that their life can be extended because the diode junction
    actually runs cooler under pulsed conditions. Does anybody know the
    optimum voltage, frequency and duty cycle to use?

    I understand that white LEDs are really blue LEDs with a phosphor
    coating on the inside of the bottle and these cannot be pulsed above
    about 5kHz, because although the LED can flash much faster, the
    phosphor cannot keep up and the LEDs change colour.

    Can anybody offer any help?
     
  2. Pulsing any light source, including LEDs, does NOT make the average
    light level higher for the same average power input - unless there is
    some characteristic of the source that makes them fundamentally more
    efficient at higher current. You cannot fool Mother Nature.
    It doesn't matter -- see above.
     
  3. Guest

    Ok well I was looking for something else but I was able to find spec
    sheets on your type of LED's(ie. InGaN) and they recommend 30% duty
    cycle and 1kHz and 100mA of current. But I also found the math
    calculation's to consider anyways.
    Also found simple power supply design
    Recommended power supply DESIGN for LED's will take into account for
    temperature.

    http://literature.agilent.com/litweb/pdf/5989-0461EN.pdf
    http://literature.agilent.com/litweb/pdf/5091-9704E.pdf
    http://literature.agilent.com/litweb/pdf/5963-7544E.pdf
    Products homepage
    http://www.semiconductor.agilent.co...fijdio.0&sProdNum=HLMP-CW38-SV000&Section=LED
     
  4. Mentions max. recommended peak and max. recommended average currents and
    ratio of these works out to pulsing at 30% dusty cycle. However, I am
    familiar with this sort of LED and when the instantaneous current is
    around 5 mA or more, you usually get more light from a given average
    current with steady DC rather than pulsed operation.
    Shows efficiency peaking at 20-30 mA instantaneous current for the LED
    types in question (obvious to me other than InGaN types, probably GaP,
    GaAlP or InGaAlP or the like. A major clue is forward voltage as a
    function of current. InGaN is different by having maximum efficiency at
    lower currents.)
    This is a temperature compensation circuit. I did not see any claims of
    efficiency improvement from pulsing, especially for average current around
    "typical" or "maximum" of any LED type or even of any common
    sort/kind/type/whatever.
    Homepage for that manufacturer's products, with no claims anywhere in nor
    linked therefrom that any of their LEDs have significantly better luminous
    efficacy when pulsed than when fed steady DC when the average current is
    at "typical"/"characterized" level or at maximum level or anywhere in
    between.

    More on the truths and myths of pulsing LEDs for better luminous
    efficacy is at:

    http://www.misty.com/~don/ledp.html

    - Don Klipstein (http://www.misty.com/~don/ledp.html
     
  5. Guest

    Oh I personally would make my life simple and would power the LEDs to
    the manufactures recommendations and would just bias them using
    15-20mA. However if I needed to save power and wanted light I would
    then pulse the LED's. No manufacture claims more light by pulsing for
    the human eye. However, the human eye can't see when and LED's is on
    or off when plus greater than 60Hz 50% duty cycle min . It's a
    trick to save power. Not to make LEDs brighter for human eye. I was
    just searching for one thing and found the specs that might help out
    the original post and should have said it was impossible with out
    damaging the LED.
     
  6. Why not just lower the current to save power? Pulsing does not save
    power for the same average light level unless the LED is more
    efficient at the higher pulse currents. See the discussion on Don's
    Web site, as listed in his message.
     
  7. R.Lewis

    R.Lewis Guest

    Victor, you really should know better!
    Once someone believes that waggling around with the supply to an led confers
    some magical power saving properties due to the human eyes characteristics
    and/or special (secret?) properties of the leds, you are *never* going to
    change their mind.

    But then again,maybe it is best to keep trying.....
     
  8. On Mon, 9 Feb 2004 21:51:37 -0000, "R.Lewis" <h.lewis-not this
    You are, sadly, correct.
     
  9. Guest

    Victor, you really should know better!
    Thanks for correcting me.
     
  10. N. Thornton

    N. Thornton Guest

    Its weird how tenacious this LED pulsing myth is.

    Regards, NT
     
  11. Isn't that true of all myths :)
     
  12. R.Lewis

    R.Lewis Guest

    You would be surprised at the number of products I have experienced that
    modulate the current to promote efficacy/increased output.
    Some of the reasons (explanations), from serious 'engineers', are quite as
    bizarre as the implementations thereby produced.

    It does, however, help pay the bills.
     
  13. Dr. Dagor

    Dr. Dagor Guest

    I need to make some hyperbright/superbright LEDs even brighter.It sort of sounds like you already have the LEDs. If that's the case
    you are limited to whatever current you can push through them until
    the smoke test fails and all the smoke is released.

    In fact, you should be able to heat sink the little buggers and crank
    50 ma through them. The traditional 3mm and 5mm bullet packs are the
    WORST for this sort of treatment. Several packagers, like Microsemi
    and Lumileds make SMD and DIP packages that will dissipate the
    junction heat much better than the polycarb bullets, and which
    therefore can handle more juice.

    As far as pulsing is concerned.... Any diode will let you bang on it
    really hard once or twice. But if you pulse them at frequencies high
    enough that the eye sees the light as continuous (above about 50 Hz)
    the LED's junction temp will be a function of the integral of the
    current over time and will be the same for pulsed and DC. So unless
    you are building a strobe flash or a bike headlight flashing at about
    0.5 Hz, don't bother with pulsed DC.

    And here is another piece of bad news. LED output decreases with age
    on a curve that is roughly proportional to hours * mean junction temp.
    If you run the LED hotter, it will dim faster.
     
  14. Leeper

    Leeper Guest

    Why not use 1W, 3W, or 5W LEDs from www.luxeon.com instead of the 0.072W
    LEDs that you
    are using?
     
  15. N. Thornton

    N. Thornton Guest

    Is that true for other colours as well as whites?

    Regards, NT
     
  16. R.Lewis

    R.Lewis Guest

    Yes.
     
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