LED and conventional diodes

Discussion in 'General Electronics Chat' started by Webby, Jun 17, 2008.

  1. Webby

    Thread Starter Active Member

    Jun 15, 2008
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    Correct me if Iam wrong but does a convential diode work the same as a LED, producing light as the current flows but is consumed by the diodes black material type shell?
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Well, they have vaguely similar characteristics in that they're PN junctions, but don't produce visible light.

    However, most BJT (transistors) ARE light sensitive; if they weren't in a light-proof package, they would conduct as a function of the light intensity shown on them.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    Regular diodes don't produce light, LEDs were the result of decades of research to improve this characteristic to the current state of the art. Side note, LEDs are transducers, they will generate a small amount of voltage when exposed to light, very small.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    You can use an RGB LED in conjunction with a uC that has an ADC as an el-cheapo light & color meter.
     
  5. cumesoftware

    Senior Member

    Apr 27, 2007
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    Conventional diodes do produce light. They produce low energy IR radiation, which is light, though not visible. Conventional diodes and LEDs behave the same, but since LEDs are made of a different material, the recombination of electrons and holes is more energetic, producing electromagnetic radiation with a shorter wavelength.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    I've seen chippies under a microscope that were wired incorrectly light up like a city from altitude. They were burned out afterwards of course. I suspect you'd have trouble measuring any light out of a conventional diode, one of the conditions for a conventional PN junction to glow is it has to be stressed, like that chippie I mentioned (it was a 7400 series flip flop in a microelectronic package). I'll concede there might be something there, but it will be orders of magnitude dim, to the point of undetectability.
     
  7. cumesoftware

    Senior Member

    Apr 27, 2007
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    I'm referring to normal conditions and not to overload conditions where the light you see is due to excessive heat and not due to electronic recombination.

    There is a silicon diode, of which I don't know the reference, that is designed to emit microwaves.
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    This wasn't heat, it was stressed junctions, which is what got researchers thinking about LEDs in the first place. There was heat, elsewhere. Ever work with microelectronics? You get to see raw chip stock working. I've see the heat side, there is a difference. I've seen diodes heat up as a block just before they melt the gold wire, they don't glow all at once, you can see the glow as a wave starting on the junction or base and working its way across.

    That job was fun while it lasted, about 15 or so years on that end of it.
     
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