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led's

Discussion in 'Electronic Design' started by lynn, Sep 25, 2003.

  1. lynn

    lynn Guest

    Dear All,

    just curiosity, maybe it seems stuped but I want to know something
    about led's.How much energy does an led emit and what determines the
    color of the light?

    Thanks in advance

    ps if you know any sites where I can find more information about
    led's, let me know!

    Lynn
     
  2. Ben Pope

    Ben Pope Guest

    That depends on the LED.

    I think it's the bandgap that determines the wavelength - and thats affected
    by the materials and dopants used. You can get visible ones, infra-red,
    ultra-violet, laser...

    There must be loads of websites out there...

    Ben
     
  3. I'm not sure about energy or know of websites describing them, but the color
    is defined by the bandgap (distance between the valence and conduction
    bands) of the semiconductor which it was made out of. Semiconductors which
    have a large bandgap, like Indium-Gallium-Nitride (InGaN) impart more energy
    into the photon and therefore emit blue or violet photons. Gallium-Arsenide
    (GaAs) LEDs, having a smaller bandgap, are on the other side of the visible
    spectrum emitting red or infrared light. Wide spectrum LEDs, like white
    colored ones are actually a combination or red, green, and blue LEDs packed
    closely togethor, or, I believe much more commonly, an InGaN LED coated with
    phosphors.

    In case if you're also curious, Silicon makes aboslutely lousy LEDs, even
    though it is significantly cheaper semiconductor to manufacture. Almost all
    of the energy you put into it gets wasted heating up the crystal lattice. I
    might be wrong, but if I remeber correctly, the photons which do get emitted
    are blue.

    Howard Henry Schlunder

    in message
    news:...
     
  4. Ben Pope

    Ben Pope Guest

    Yeah, thats why they're rarely used for optical applications, despite the
    cost consideration.
    Thats possible, although true blue LEDs are a relatively new thing.

    Ben
     
  5. Fred

    Fred Guest

    Ultra-violet LEDs? Where?
     
  6. Well, a good place to start is The Led Museum:
    http://www.ledmuseum.org )

    And of course Don Klipstein's Web Site:
    http://www.misty.com/people/don/index.html


    Søren A.Møller
     
  7. Ben Pope

    Ben Pope Guest


    BivarOpto make them:

    http://www.bivar.com/default.asp?p=products&c=UV LEDs

    Toyoda Gosei make some too, can't find them on their website though.

    RS do them:

    Metal Can: E1L5M-3P0A2 and E1L5M-4P0A2
    SMD: E1S19-0P0A7

    Ben
     
  8. Fred

    Fred Guest

    The shortest wavelength LED using your link is 395nm. This would be classed
    as violet rather than ultraviolet. The visible range is normally taken to
    be nominally 400nm to 700nm.
     
  9. Ben Pope

    Ben Pope Guest

    The SMD ones are 374-401nm
    Metal can are: 374-392nm

    Here's one at 350nm:
    http://www.roithner-laser.com/All_Datasheets/LEDs/RLT350-30.pdf

    Which I think can be classed as NUV if nothing else.

    Ben
     
  10. Ian Stirling

    Ian Stirling Guest

    Is there anything in the near future at near 250nm (germicidal?).
     
  11. Jim Yanik

    Jim Yanik Guest

    IIRC,All Electronics was selling 12 mW UV leds for a couple of bucks each
    awhile back,not a bad price.
    Or was it ALLtronics? AAACK!
     
  12. www.ledmuseum.org and go to the links, www.nichia.com sells them, etc.,
    etc., etc.,...



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  13. Perhaps you are thinking of silicon carbide blue LEDs. Back in 1907 it was
    discovered that silicon carbide could be made to electroluminesce. The
    sample used back then probably contained some built in pn junctions.
    Silicon carbide LEDs tend to have hideously bad luminous efficacy,
    especially the ones that were briefly available around the early 1970's.
    Silicon carbide is a wide bandgap semiconductor. Dim but practical blue
    LEDs have been available with output peak wavelength of around 470nm. They
    have since been greatly superceded by GaN blue LED technology.

    Plain silicon does indeed make for terrible LEDs. Although the energy
    bandgap is theoretically compatible with LED light production, silicon is
    known as an "indirect semiconductor." One of the consequences of being an
    indirect semiconductor is hole electron recombination doesn't normally
    produce photons of your anticipated wavelength, but instead produces phonons
    (as compared to photons) which are quanta of sound pressure waves, or in
    other words lattice vibrations which is heat. Silicon doesn't produce any
    particularly meaningful number of photons of any wavelength practical for
    LED technology (at least until you start cranking the serious juice through
    them and they start producing light just like any good blackbody radiator
    should... but you aren't supposed to do that...).
     
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