different coloured LED's?

Discussion in 'Homework Help' started by Sbaraka, May 12, 2010.

  1. Sbaraka

    Thread Starter New Member

    May 12, 2010
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    Why is it that different coloured LED's have different rates of switching on and off?

    i have tried very hard to find the answer via research on the internet, visited many sites about LED's, but have been unable to find out the answer to this question. :confused:

    so of course anybody who could explain it, or post a link to a website which does, it would be greatly appreciated.
    thank you. :)
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    what do you mean by rates of switching.
    You can find answers only if your question makes sense.
     
  3. Sbaraka

    Thread Starter New Member

    May 12, 2010
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    thanks for replying. well i mean exactly that, the speed at which the LED flicks on and flicks off. so how soon after getting electricity does the LED turn on. so why is it that when in an exact same astable multivibrator circuit do green LEDs flicker faster than red LEDs
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    Post the circuit and perhaps we can tell.
     
  5. retched

    AAC Fanatic!

    Dec 5, 2009
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    They dont. The switching speed is not a cause for flicker. It is the duty cycle.

    You want to look at the datasheets for your different color LEDs. They have different Vf (forward voltage, or voltage drop) and some require more current to appear as bright.

    You may not want to use the same astable mv for both leds, as they may require different operating voltages or current. If you found a green and red LED of the same specs, there would be no difference (noticiable. A few nM of wavelength maybe) It could also be your eyes ability to perceive color.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    LEDs respond to current, they do not control it. Their may be minor speed differences, but given that LEDs are meant to provide light typically for humans, who can't tell 1 or 2 milliseconds apart, 1 or 2 nano or microseconds doesn't mean squat. My feeling is the questions is meaningless.

    If an LED is fed DC it doesn't flick on or off, it provides continuous light.

    LEDs, 555s, Flashers, and Light Chasers
     
  7. Markd77

    Senior Member

    Sep 7, 2009
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    I'm guessing that the LED is part of the multivibrator circuit and so the different forward voltages change it's frequency.
    Post the circuit.
     
  8. Sbaraka

    Thread Starter New Member

    May 12, 2010
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  9. retched

    AAC Fanatic!

    Dec 5, 2009
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    the capacitors will charge at different rates after the LEDs. This is due to the different voltage drops from the different LEDs.
     
  10. Sbaraka

    Thread Starter New Member

    May 12, 2010
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    oh that is so obvious, i can't believe i didn't figure that out. im so ashamed lol. thanks a lot for the help
     
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