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Thread: Strobes: Xenon vs LED

  1. #61
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    Critically damped strobe tubes with a tuned inductor are about 250 to 500 microseconds. Long tubes without a inductor, or with a undersized inductor are about 1.5 milliseconds. I had to measure that all the time when measuring flashlamp pumped Yags, and when making strobes for lab video systems. Damped lamps have a fast rise time with a smooth curved fall. Undamped lamps ring and have a exponential decay to just above the conduction threshold.

    The Leds can go that short, but designers like the "Punch" from leaving the dimmer leds on, as you suspect. The Leds are usually Square wave, without the bright flash that that is on the leading edge of the Xenon. That bright leading edge is what your missing on the leds. So they run them long. If you don't have the punch, you go to the long pulse.


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    Steve
    Last edited by mixedgas; 06-17-2014 at 17:03.
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  2. #62
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    I have no idea whether or not the ADJ MegaFlash strobes are damped or not. I know you had said, at one point, that your lab was using them for photography so you'd prbably know. Regardless, these LED strobes that I am using are far slower. I was judging the flash time based on my ceiling fan and absolutely, the xenons were "stopping" the fan in a perfect image while the LED strobes were blurring the fan blades with each flash. I'd imagine some of the really high priced LED strobes are down around the flash time that you are talking about. For the price and what I am using these for, they are pretty nice. I still don't see the draw for LED strobes just yet as far as trumping xenon because it certainly ain't the price! Perhaps the power requirements along with the low voltage of LED. Anyway, thanks for your input, Steve!
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  3. #63
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    Default strobing LEDs

    Quote Originally Posted by absolom7691 View Post
    I finally found an LED strobe that is worth it's weight. Has anyone else heard of ColorKey? This is the first I have seen or heard anything about them. http://www.amazon.com/ColorKey-6x10W...s=colorkey+zap

    I bought two of these, expecting the worst and was very pleasantly surprised. I would say these are roughly 75% of the brightness from my ADJ MegaFlash stobes. Now, of course that is subjective since the "on time" of the LEDs is probably 10x longer (maybe more) than my xenon strobes so I may be perceiving the light as brighter. Not sure. These 60W LED strobes are damn bright, I can tell you that! The only downside to LED strobes, that I have found, is the "stop action". It is still not there. I don't know the "on time" for xenon but it is a hell of a lot shorter than LED and thus, gives that perfect "stop action". LEDs aren't there yet. But if you're after a nice bright flasher, these will fit the bill. These ColorKey Zaps are going to be added to my haunted yard this year to suppliment my ADJ MegaFlashes. These have about the same footprint as an ADJ MegaFlash. Also, they are always cyclic, there is no "full on" blinding effect.
    ================================================
    When doing the Luxor job and a more recent flash project we were concerned about the instantaneous current capabilityof the LEDs. Being conservative, I limited it to twice constant current rating. I never did thorough research on this, and better peak current LEDs may be available now. Also, remember if you're using white, the phosphor may saturate at high illumination. In that case, use a set of color LEDs

  4. #64
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    I have not used one in three years. I don't work in that lab now.

    Megaflash is a long pulse. Its a little different. It has a very small capacitor to start the tube current , then the tube is shorted across the AC line voltage . The tube extinguishes when the line cycle almost passes through zero. Current through the tube is controlled by when it fires with respect to the line phase. There is a series inductor to somewhat limit current. Memory is fuzzy, but I believe for the most of the timing the tube fires on the last 90' of the waveform either side of the zero crossing. .

    So they basically use the lamp as a Thyratron Tube across the AC line. The lamp fill pressure is high enough that it has a positive Delta I over a small Delta V , so it probably self limits to some extent.

    SO 16.6 mS for a line cycle, /4 for 90 degrees, means ~4.1 mS maximum on time, divided by 16 levels = ~260 uSec steps. That is theory, but in reality the step size was non-linear and binary... If My memory is very fuzzy, you could double those numbers for not quite 180' of line phase.....

    Very interesting Patent to read on this concept, and nice because there is no large, expensive, capacitor.

    I'm not up to date on the modern devices, but the White Lumileds and White Cree 350 and 750 mA parts that I was using for lab strobes four years ago did not like prolonged Overdrive. If the bond wires did not snap, the phosphor degraded rapidly. I'm sure that has been fixed by now.

    10 Amp single chip Leds were not in production till a year after I left the lab. I was aware of them, but could not get them till a year later. I have two of the Phlatlight 9 Amp red Leds, I should try strobing them some day and measure what I get. Phlatlight/Luminus warns they need a long softstart, so dumping a capacitor into them would probably be bad.


    Steve
    Last edited by mixedgas; 06-18-2014 at 13:58.
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    I went back through this thread and was surprised not to see this: http://www.chauvetlighting.com/strike-882.html

    It's no Atomic or Diversitronics, but they are pretty fucking bright.

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    I use 5 cell smd and 3 cell smds identical to the Neo neon flash 150's and 300's. Definitely don't have the punch of a zenon but they seem warmer and more of a pure white with zero after flash that zenons have. Not all led strobes are equal though and there are some horrendous ones out there. SGM do some really nice ones but the price is high for that niceness. I personally like smd strobes and if your creative with positioning ( i fly mine pendant style) you can create effects that a single source zenon just can't do. Cycle time on mine are brilliant and they don't need a 16 amp supply!
    In fact I can run 6 of the 5 cells off 13 amp!
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    I went back through this thread and was surprised not to see this: http://www.chauvetlighting.com/strike-882.html

    It's no Atomic or Diversitronics, but they are pretty fucking bright.
    Actually, I think that is the Chauvet branded version of the Showtec Technoflash (or whatever its called) that I couldn't find any info on last year, and not sure if it ever made it to market (in the UK at least). certainly based on the 5050 SMD sources
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    Norty,if your in the market for smd strobes I'll send you a supplier we use in Hk.Really high quality and seriously competitive prices, for what eBay resellers are charging is ridiculous. Finding a good supplier/manufacturer is 90% of the battle.
    lighting the way since 89

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    Send away please
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    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

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    I'd be interested as well please mr Blu;-)
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