LED watt calculation

Discussion in 'General Electronics Chat' started by Lolgogo, Aug 23, 2013.

  1. Lolgogo

    Thread Starter New Member

    Aug 16, 2013
    11
    0
    Hello!
    A few days ago I was shopping on eBay and found 3watt yellow "star" leds.
    On the description page, it was rated at 2.0volts - 2.4v and 750ma. If I multiply those , I get about 1.8 watts.
    Am I doing something doing wrong with the calculation?
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    Nope. The discrepancy rests elsewhere.
     
  3. snowdrifter

    Member

    Aug 13, 2013
    43
    1
    Most likely it's the typical overrated chinese (or whatever) marketing.


    Over in "my realm" of car audio,we deal with this all the time. You'll buy an amplifier rated for 1100 watts but only has 30 amps worth of fusing and can only put out a measured 2xx watts. Rounding up, inflating numbers, etc to make a product look better than it really is
     
  4. Lolgogo

    Thread Starter New Member

    Aug 16, 2013
    11
    0
    Aww... So the maximum is only 1.8 watts I guess...
     
  5. RichardO

    Well-Known Member

    May 4, 2013
    1,231
    382
    I have seen some really awful data sheets for Chinese LED's. Some were so bad that there was no way to know what they were trying to sell. I think a lot of the problem was in the translation to English.

    Giving them the benefit of the doubt, it may be that it is simply a typo caused by editing a data sheet that was originally for a white LED -- 750 mA times 3.6 volts is almost 3 watts.
     
  6. Metalmann

    Active Member

    Dec 8, 2012
    700
    223



    I remember just a few years ago, there was a big stink about the HP ratings of small combustion engines.
    Such as rating a 12 HP, @20 HP, etc.
     
  7. Lolgogo

    Thread Starter New Member

    Aug 16, 2013
    11
    0
  8. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    The 3W is almost certainly what is called an "abs max" rating for power dissipation for the device which is defined primarily by the die size and package type. Obviously, the nominal operating conditions better be less than the absolute maximum ratings or it smokes. The power is not what you care about, it's the luminance (brightness). In fact, if it puts out the same light at a LOWER power that's actually better because it runs cooler and eats less power.
     
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