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Thread: White LED phosphor persistence??

  1. #1

    Default White LED phosphor persistence??

    Does anyone know the persistence times of the phosphors used in typical white LEDs? I built a strobe circuit a few years back, when ultrabright red was the newest thing, and was thinking of a newer version with white LEDs. I'm afraid that the white ones may not turn off fast enough, though, due to the phosphor continuing to glow after the current stops.

    I guess I could use separate red, green, and blue LEDs, or even one of those nice packages with multiple chips in it, but it would be easier if I could get away with using white.

  2. #2

    Default Re: White LED phosphor persistence??

    I don't think you can use color leds to make the color of white led. There has been discussion about the possibilities of using colored leds to make whites but the majority said it is impossible.
    regarding the phospor persistence, i don't think that will be a problem though. Take for example Eternallight products. The leds was made to strobe fast enough, but you still can see that it is strobing. I guess it all depends on the speed of your strobe?

  3. #3
    *Retired* The_LED_Museum's Avatar
    Join Date
    Aug 2000
    Federal Way WA. USA

    Default Re: White LED phosphor persistence??

    I think it will depend a lot on strobe speed, phosphor persistence, and persistence of vision.

    The phosphor persistence of white LEDs is pretty long, but probably no more so than your typical color TV or computer monitor. I don't have anything to measure this with though, so I cannot give you a chart of phosphor decay of white LEDs.

  4. #4
    *Flashaholic* James S's Avatar
    Join Date
    Aug 2002
    on an island surrounded by reality

    Default Re: White LED phosphor persistence??

    Just how fast are you trying to strobe things? For anything where a human eye can preceive the flashes there certainly wont be a problem. I do have a few lights where a barely perceptable glow remains in the light for a few moments after the power has been switched off, but nothing like a fade out or something that would mess with the strobe. If you're trying to stop motion a 36000 rpm engine shaft then you might have a problem, but for anything else I think you should definitely give it a try.

    Some lights, like my arcAAA have a capacitor in them or something that makes them fade out instead of switch right off, but thats part of their circuit, not the LED.

  5. #5

    Default Re: White LED phosphor persistence??

    [ QUOTE ]
    James S said:
    Just how fast are you trying to strobe things?

    [/ QUOTE ]

    I was using it to stop the motion of a continuous stream of bubbles for analyzing a "device" I was building at the time. The flash rate was maybe a few hundred hertz, but the flash had to be pretty short (and bright) to get sharp images of the moving bubbles. I found the thing actually pretty usable for visualizing the bubbles, although the LEDs I had at the time were fairly weak by today's standards, so it had to be photographed in a dark room.

    My thought at the time was that a battery-powered LED-based strobe light would be pretty cool for general "Doc Edgerton" experiments, but they were not quite bright enough. They're certainly closer today, especially with luxeons. I'd bet the phosphor would make the white ones too slow, though.

    Along the lines of creating white light with multiple LEDs, what about using more than just the r, g, and b, and filling in the spectrum with whatever LEDs are available. I bet with maybe 6 of them, you could fill out a pretty good spectrum of light. You just need to get the right ones.

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