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Blue LEDs? when did that happen?

Discussion in 'Electronic Basics' started by guy-jin, Sep 28, 2004.

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  1. guy-jin

    guy-jin Guest

    I ran across an old electronics book, the beginning chapters of which
    deal with light emitting diodes. it described the problem of blue
    LEDs; IIRC, the distance between the poles determines the color, but
    when you get them far enough apart to make blue light, current no
    longer flows between the poles.

    Am I remembering correctly, and how was the problem solved?
     
  2. CBarn24050

    CBarn24050 Guest

    I ran across an old electronics book, the beginning chapters of which
    Must have been an old book, the problem was allways getting the right material
    to make them, now we have UV leds as well. The Xray led is still a way offf yet
    though.
     
  3. By one man Shuji Nakamura

    http://www.businessweek.com/1999/99_24/b3633068.htm

    Adam
     
  4. Bob

    Bob Guest

    Austin,

    Many things have changed since you were frozen in the 60's. And yes,
    Liberace was gay.

    Bob
     
  5. John Larkin

    John Larkin Guest

    It's the semiconductor bandgap, not the physical dimensions, that
    determines the color.
    I think the Cree SiC blue led's predated these, but they were
    horrendously inefficient: they needed something like 3 volts, 50 mA to
    be a decent panel indicator. Paralleled 74S38s + 27 ohms from 5 volts!

    But where do they use blue traffic lights?

    John
     
  6. John Larkin wrote...
    The modern high-efficiency blue (and white) LEDs also require 3V, as
    determined by the band-gap voltage like you said. But they give more
    light at lower currents. These days all the rage is purple LEDs, for
    a much much more impressive light-color sensation.
    Isn't purple needed for low-rider under-the-car lighting?
     
  7. Japan, I think!
     
  8. John Larkin

    John Larkin Guest

    Every couple of years we have to write ECOs to change the
    current-limit resistors on a lot of our products that use blue LEDs.
    They keep getting more efficient, and customers complain that our
    front-panel lights are blinding them. We must average about 5 mA these
    days, down from 50 with the old Cree parts.

    John
     
  9. Don Bruder

    Don Bruder Guest

    Blue plus yellow equals green...
     
  10. guy-jin

    guy-jin Guest

    Not that I ever saw.
     
  11. John Larkin

    John Larkin Guest


    Is that somehow better than using green?

    John
     
  12. Don Bruder

    Don Bruder Guest

    Doubtful that it's "better", but... <shrug>

    (And never mind the fact that I brain-farted on the fact that we've had
    green LEDs seemingly forever - Was thinking in terms of "Damn... Only
    have red and yellow - Gotta "build" green if using LEDs, and the only
    way to do that is yellow plus blue.")
     
  13. Maybe this came from the Japanese having the same word for the colors
    blue and blue-green - something that I heard is true.

    - Don Klipstein ()
     
  14. Ever mix the light from a blue LED with the light from a yellow one?
    It's certainly not green.

    - Don Klipstein ()
     
  15. They cover too much of the visible spectrum to have any very saturated
    color at all.
     
  16. That is so; in the Japanese Language a 'green' traffic light is called
    'blue' ["ao";"aoi"] while e.g. a 'green' leaf is 'green'
    ["midori";"midori no"]. As a result, a green traffic light and a blue
    LED are described by the same adjective which may be the source of this
    confusion - especially since the actual color of the traffic lights is
    identical to the western ones.

    Chris
     
  17. Don Bruder

    Don Bruder Guest

    Can't say I have. To be honest, I don't think I recall ever even having
    a blue and a green LED in the same room together, let alone trying to
    mix 'em.
     
  18. Fred Bartoli

    Fred Bartoli Guest

     
  19. Gordon Youd

    Gordon Youd Guest

    I once had some LEDs which gave all the colours of the rainbow including
    xray, I put them directly across the mains, WOW!!! I lost my cat the same
    night.

    Gordon.
     
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