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Thread: Brightness variance is NORMAL

  1. #1
    Council Member Novastar's Avatar
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    Mar 2007
    San Jose / San Francisco, CA

    Default Brightness variance is NORMAL


    Ok... I want to make a short but useful post... and it's about LED brightness.

    1. Providing an LED with its "manufacturer listed" forward voltage may not yield "the brightest" the LED can be. In some cases, to achieve the maximum continuous current... you must provide a bit more than the fwd v.

    In other words--if the fwd v = "3.85v", and they list the max cont. curr as "1000mA"... you may need to give the LED 4v (maybe even more) to achieve the 1000mA. Keep it in mind.

    If you wish to overdrive (say @1200mA)... you'll need even more voltage.

    Bottom line: voltage and current are RELATIONAL.

    2. You have a Luxeon V Blue LED, bin 1. You have ANOTHER Luxeon V Blue LED, bin 1. You bought them from the same company... and you even think they came from the same "batch" in the factory (like, maybe they were attached at the PCB "star" sides and you separated them). So--as far as you're concerned, you think they are identical.

    You test both, feeding each EXACTLY the same current & voltage.
    For the test--you don't use any driver boards--you just go direct drive.
    You put both into blades, each EXACTLY the same length, blade film/diffuser and tips, etc.
    Optics are the same degrees... and blade holders too.

    "Somehow"... one is brighter and more vibrant... and the other is just "ok" or "so-so". HOW COULD THIS HAPPEN?!?!?

    This is part of the luminous flux of an LED--which is a property of the overall binning... but is also SUBJECT TO VARIANCE. Just like most anything out there.

    Different manufacturers have different levels of "acceptance" for LEDs during the binning process... but I can tell you something: they *ALL* allow SOME variance.

    This is precisely why you'll find all sorts of seemingly "conflicting" stories out there with people who are saying:

    "My Lux III blows away my Lux Rebel (1-up)..."
    "That's weird. My friend's Luxeon V green is kinda--well--weak... but my Luxeon V blue is crazy bright!"
    "Hmm... I tested 4 similar red LEDs, and they all have some significant differences in brightness."
    ...and so on...

    Additionally, when you start figuring in:

    * The FACT that these LEDs were never meant to illuminate a bloody "star wars lightstick tube" with diffusion film and mirror tips (and thus--a lot of light is actually LOST--yes, that's right--no matter how awesome the optics are)
    * Someone takes a photo of their saber and compares it to yours (differing light levels, camera biases, quality distance, flash, etc. etc. etc.)
    * You're using optic type X... he's using optic type Y...
    * Your blade is ______ while his is ~~~~~~.
    * You're using a PWM style driver + Li-Ion cells... he's using no driver, a resistor, and Ni-Mh...

    ...what you get is A PERFECT MESS.

    What is the lesson? Hmm. No real "lesson". But just keep in mind that variety is the spice of life (and LEDs)... and you're rarely going to find a "definitively" bright LED where you compare 100 of LED type X vs. LED type Y--and come up with some kind of magical "absolute" definitive answer on what trumps what.

    Last edited by Novastar; 05-04-2010 at 07:52 PM.
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  2. #2


    The amount of variables does seem to approach a zillion sometimes. I recently found specs of dust on led domes & lenses messing with light output. The parts that need to be very clean, seem to attract dust like a magnet!

    Also watch out for the invisible ESD phenomenon which can reduce led output & you would never know it. I touch the metal backside of my computer or other ground source frequently when handling electricaltronics type stuff.

  3. #3


    Thanks for the post Novastar.

    I think this is equally useful for new saber builders and experienced ones alike.
    Follow Your Bliss

  4. #4


    I've noticed this from time to time. A MHS saber I made for my friend (I think it's even listed in the gallery now) has one of the brightest LuxIII blues (bin 3 I believe) I've come across. It's super bright and gorgeous and I keep telling him that I'm gonna secrectly swap it one day.

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