How fast can White LEDs blink?

Discussion in 'General Electronics Chat' started by SunSeaSkyy, Feb 25, 2016.

  1. SunSeaSkyy

    Thread Starter New Member

    Feb 25, 2016
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    Does anyone know how fast a generic White LED can be made to blink? I know that bare LEDs can blink up to a MHz or more. But the white phosphor coating on White LEDs slows the effective blink rate because of the rate of decay of the phosphor glow.
    Is it tens of Hz? Hundreds of Hz? KHz?
     
  2. #12

    Expert

    Nov 30, 2010
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    Here's one that is rated for a forward pulse of 50 useconds. That's 50 KHz for a 50% duty cycle if my calculator is working right.
    I'm sure there are faster LEDs. This is just what I picked up in a 5 minute search.
    Fiberoptic communication suggests hundreds of megahertz, but I don't know if that's anywhere from infrared to ultraviolet.
     
  3. ronv

    AAC Fanatic!

    Nov 12, 2008
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    They are still pretty fast.

    upload_2016-2-25_17-57-8.jpeg

    http://forum.allaboutcircuits.com/threads/led-afterglow-time.118776/#post-939092
     
  4. #12

    Expert

    Nov 30, 2010
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    Can't read the labels on your graph.:(
     
  5. ronv

    AAC Fanatic!

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    Yea, me either. :cool:
    I added a link.
     
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  6. SunSeaSkyy

    Thread Starter New Member

    Feb 25, 2016
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    Thanks much for taking the time to respond. As someone else mentions below, the vertical scale does not make sense to me and has no units.
    Regardless, it shows me that phosphor coated LEDs are not that much slower than bare ones. A KHz seems to be no problem.
     
  7. KJ6EAD

    Senior Member

    Apr 30, 2011
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    Multiple IR wavelengths, mostly around 1500nm.
     
  8. WBahn

    Moderator

    Mar 31, 2012
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    I think that's a different animal entirely -- they aren't using phosphored light sources for fiber optic communication.
     
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  9. AnalogKid

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    Aug 1, 2013
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    If...
     
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  10. #12

    Expert

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    Yep. Today my calculator gets a completely different answer...like 10 KHz.
    I suspected something was wrong yesterday!:(
     
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  11. MrAl

    Well-Known Member

    Jun 17, 2014
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    Hi,

    Fios uses lasers not LEDs.

    Note that some LED specs specifically state that they should not be pulsed. Mainly the higher power type LEDs like the Cree. Maybe a lower peak currents it would be ok, but never tried that.

    Some white LEDs are pulsed with very fast pulses, but the main thing is to get the rise and fall times fast so as to not burn out the LED (using high current).
     
  12. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    10 kHz is what I calculated yesterday... but then I saw your first calculation and then I thought that something was wrong with me! :confused:
     
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  13. ian field

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    Oct 27, 2012
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    If it has to be white - an RGB led is as fast as the slowest bare LED in it.

    Someone on this forum has said they got a clean square wave on a photo sensor at 1kHz.

    Green is a good compromise if you find phosphor persistence too slow.

    The original white LEDs are/were blue with a yellow phosphor - probably not all that fast, I think they might be phasing in UV LEDs with white phosphor, which are probably faster.
     
  14. #12

    Expert

    Nov 30, 2010
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    Everybody makes misteaks.:p
     
  15. cmartinez

    AAC Fanatic!

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    ... and thanks to you, now I'm hungry.... again ...
     
  16. SunSeaSkyy

    Thread Starter New Member

    Feb 25, 2016
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    Thanks for the info. I am not seeking the fastest. Just what to know what I can expect from a generic white LED. My target freq. is 120 Hz so I'm trying to determine if I'll be ok with any old white LED, or if I will need to pay close attention to get one with right phosphor.
     
  17. SunSeaSkyy

    Thread Starter New Member

    Feb 25, 2016
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    Thanks everyone for the excellent info. I'm learning a lot.
    I am not seeking the fastest white LED. Just what to know what I can expect from a generic white LED. My target freq. is 120 Hz so I'm trying to determine if I'll be ok with just about any white LED, or if I will need to pay close attention to get one with right phosphor.
     
  18. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Really? Unless there's something very weird about the device physics, an LED is not a transistor and doesn't saturate, so there is no extra power dissipation during the transition region from off to on that is greater than the power dissipation at full on.

    ak
     
  19. #12

    Expert

    Nov 30, 2010
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    You could have said that in the first place and saved us all a lot of time. Anybody with a year of experience would know the answer without doing google searches.
     
  20. ian field

    Distinguished Member

    Oct 27, 2012
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    Apparently automotive LEDs are PWM driven, and strobe if you catch them at a glance.

    Probably most of those are red or amber - but a few are white.

    120Hx is probably OK with the blue/yellow phosphor variety.
     
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