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Making yellow from bi-color (red/green) LEDs

Discussion in 'Electronic Design' started by Joel Kolstad, Feb 15, 2007.

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  1. Joel Kolstad

    Joel Kolstad Guest

    Just curious... if you're trying to use a bi-color (red/green) LED to make
    yellow, how well does it work using an LED with a clear "lens" along with a
    (clear) light-pipe (mounted above the PCB, going through the case)? I've used
    diffused LEDs in the past to do this with no problem, but I'm thinking that
    with a clear lens there won't be enough mixing of the red and green and the
    user will just perceive the two distinct colors rather than yellow as
    intended. Thoughts?

    Given a choice of packages (e.g., 1210 vs. 0605), presumably I'd want the
    smallest one available so that the red and green LED chips are as close
    together as possible, right?

  2. As long as the viewer does not have a clear image of the two
    die in the LED, the light will appear to be a single color.
    The only problem with not diffused sources like this is
    that the apparent hue may vary a bit with viewing angle.

  3. Just wait till they decide to build cheaper traffic lights by using a
    single light housing, with bi-color LEDs to get Red, Green and Yellow.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  4. Joel Kolstad

    Joel Kolstad Guest

    Thanks John; I'm ordering a few to play with and see how it does. In an 0605
    package I suspect that unless you're within inches of the LED you wouldn't be
    able to discern the colors individually. (Harkening back to the time as a kid
    you put your face up to the glass and realize that there are actually three
    different colors there, all arranged in nice little triads...)

  5. Terry Given

    Terry Given Guest

    its called pixel convergence ;)

    followed by image convergence (when there are more than one pixel).

  6. mkaras

    mkaras Guest

    On Feb 14, 5:07 pm, "Michael A. Terrell"

    I recall reading someplace that the multi-position lights are
    necessary because of both color blind people and high sunlight
    conditions where even people with normal vision cannot distinguish the
    light color due to the ambient brightness.

    - mkaras

  7. That won't stop some greedy politician from trying to have them
    installed, so he can pocket the difference.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  8. Rich Grise

    Rich Grise Guest

    I was absolutely astonished when I did this the first time - I could
    resolve the individual dots, but I still saw the overall picture in
    my peripheral vision, as if it were superimposed over the little dots.

    Kinda boggled my mind, but when you're 8 or 10, that's not hard. ;-)

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