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LED - difference between red and blue

Discussion in 'Electronic Basics' started by gilbert, Jun 6, 2004.

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  1. gilbert

    gilbert Guest

    Does anybody know the difference between the red and blue LEDs? I was
    trying to make a flashing light to the front of my bicycle and tried
    to use a flasher that originally worked fine with three red LEDs. It
    doesnt show anything with the blue LEDs on,even after the original red
    ones have been disconnected. Do you guys think there is a simple way
    to solve this - like putting in a resistor or increasing the voltage
    from two to three AA batteries? The blue LEDs, four of them, now work
    fine on two batteries (AA), only, of course, they do not flash.
    Please answer me in e-mail too.
  2. Jeroen

    Jeroen Guest

    blue LEDs need more voltage to work, so I guess the flasher circuit does not
    deliver the full voltage.
  3. gilbert

    gilbert Guest

    That's strange. I tell you why. I had a functioning blue fashing
    arrangement earlier, with a cheap flasher that I bought for 99 cents
    in Los Angeles in the 99 cents store. When I bought it, it was red,
    and didn't work very well. It was not very luminous, and I figured
    that this was a bad batch, that's why they sell it for 99 cents. I
    put on the blue LEDs parallel to he existing red ones, and indeed, in
    accordance with your idea, the blue ones did not light up, while the
    red ones continued to flash.So I took off the red ones and the blue
    ones started to flash all right.
    The thing was working fine on the bicycle for several months. Then,
    one day, it stopped flashing (but if I remember correctly, the light
    was still on, continuously; I am not sure about this). Figuring that
    the flasher was broken, I threw it out, and connected the blue LEDs
    (five at the time) to two AA batteries. What happened next, was very
    strange. The light was on, but the batteries got drained (or so it
    seemed) in a couple of days. The thing seemed short circuited,
    somewhere. I suspected rain water getting in somewhere but couldn't
    find anything. Finally, I disconnected one blue LED and the remaining
    four now work just fine. That LED was somehow short circuited
    internally, partially.
    So I went out to buy another flasher for 99 cents. This one seems to
    be better, not from the bad batch that was not very bright. But the
    blue LEDs do not light up.
    Since the red lights on the new flasher are brighter than on the
    previous one, it would seem that the voltage coming out from the
    flasher is higher. Nevertheless, the blue don't light up, although
    they did with the previous, seemingly weaker flasher. So I believe it
    is not the voltage. So I was wondering if you can think of something
    else? I don't know much about LEDs, I don't even know how they work
    and what happens when you fry them.
    Any ideas, anybody? If it turns out the voltage being too low, would
    it get higher if I put three AA batteries on the input of the flasher,
    or would it just ruin the flashing circuit?
  4. Tim Auton

    Tim Auton Guest

    Did you have a current limiting resistor in there somewhere?

  5. JeffM

    JeffM Guest

    I was trying to make a flashing light to the front of my bicycle
    Forward-facing red lights on a non-emergency vehicle
    and blue lights of any kind on a non-police vehicle
    are most certainly illegal.
  6. Most blue LEDs develop a partial short if they suffer damage from static
    electricity. You can do this to a blue LED even if the static electricity
    is not enough to produce a visible or audible spark. I have also seen
    blue LEDs develop partial shorts if overheated by excessive current, but I
    doubt that happened here.
    Maybe the new flasher had less output voltage but more current or more
    efficient red LEDs than the old flasher.

    Possible the blue LEDs were damaged by static electricity or lack of a
    dropping resistor, but I doubt two AA cells will cook most blue LEDs
    without a dropping resistor. But two AA cells will have their voltage too
    low to operate most blue LEDs while a majority of their charge is not yet

    - Don Klipstein ()
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