Page 3 of 7 FirstFirst 1234567 LastLast
Results 21 to 30 of 70

Thread: Strobes: Xenon vs LED

  1. #21
    mixedgas's Avatar
    mixedgas is offline Creaky Old Award Winning Bastard Technologist
    Infinitus Excellentia Ion Laser Dominatus
    Join Date
    May 2007
    Location
    A lab with some dripping water on the floor.
    Posts
    9,164

    Default

    I'm Not a ADJ fan, but I love the MegaFlash. We actually used two of them in a lab for scientific photography. Works without capacitors by shorting the flashtube across the power line and firing the lamp at different points on the power line phase. Massive burst of light, can be disorienting. They do have duty cycle limits if your into running full blast and full out. Because its across the 110 AC line, recharge time is only 17 milliseconds :-)

    Lamps last a very long time, for what they are.

    If not, PM me, I have a few really big xenon tubes and cap banks left, but you'll need 800 volts to fire them.

    Steve

  2. #22
    Join Date
    May 2007
    Location
    Authentic Asian food area of SoCal
    Posts
    2,468

    Default

    Quote Originally Posted by mixedgas View Post
    I'm Not a ADJ fan, but I love the MegaFlash. We actually used two of them in a lab for scientific photography. Works without capacitors by shorting the flashtube across the power line and firing the lamp at different points on the power line phase. Massive burst of light, can be disorienting. They do have duty cycle limits if your into running full blast and full out. Because its across the 110 AC line, recharge time is only 17 milliseconds :-)

    Lamps last a very long time, for what they are.

    If not, PM me, I have a few really big xenon tubes and cap banks left, but you'll need 800 volts to fire them.

    Steve
    Interesting way of doing it. The ones I used to build were just voltage doublers with a trigger coil for the HV and were fired by a neon light (I guess like a a low voltage spark gap). 800V I can come up with, so many things can be done with a microwave oven transformer and a variac , but I have already bought a few of the Mega Flashes based on several recommendations. Thanks for the offer, Steve!
    Those who fail to grasp art are the ones who criticize it.

  3. #23
    Join Date
    Nov 2011
    Location
    Huntsville AL, USA
    Posts
    70

    Default

    Atomic 3k's are my strobes of choice.

  4. #24
    Join Date
    Jun 2007
    Posts
    99

    Default

    I wonder what sort of power you could get out of this using short pulses

    http://www.dealextreme.com/p/prime-1...-42806?item=14

    8000LM isn't exactly subtle, and that's its continuous rating

  5. #25
    Join Date
    May 2007
    Location
    Authentic Asian food area of SoCal
    Posts
    2,468

    Default

    Bolt 10 of those to a heatsink.... 1000W of light.... might work. A simple 555 circuit would probably do. You would need some hefty FETs, though.
    Those who fail to grasp art are the ones who criticize it.

  6. #26
    mixedgas's Avatar
    mixedgas is offline Creaky Old Award Winning Bastard Technologist
    Infinitus Excellentia Ion Laser Dominatus
    Join Date
    May 2007
    Location
    A lab with some dripping water on the floor.
    Posts
    9,164

    Default

    The problem with LEDs is the CW power IS the power you get out of them pulsed. There is no "magical" overdrive mode. This is where Xenon still rules, for now at least, the peak power is huge.

    Steve

  7. #27
    Join Date
    Jun 2007
    Posts
    99

    Default

    I don't think that's correct.

    Most LEDs have a pulsed current rating and it's higher than their CW rating.
    It's used when doing PWM to regain brightness when you have a long off-time.

    A typical high power UFO type led might be 50mA max forward current but also be spec'ed for 150mA pulse rating when duty=0.1ms and f=1khz

  8. #28
    mixedgas's Avatar
    mixedgas is offline Creaky Old Award Winning Bastard Technologist
    Infinitus Excellentia Ion Laser Dominatus
    Join Date
    May 2007
    Location
    A lab with some dripping water on the floor.
    Posts
    9,164

    Default

    The pulse rating is there, but it does not gain you much higher average brightness. If the die is hot, on phosphor based leds, the pump wavelength shifts
    far enough to defeat the extra energy. This has been debated on electrical engineering forums for years. The consensus was, on a few early leds, there was a net gain in average output power when pulsing. Later devices did not exhibit the effect, and the myth persisted.

    Debate welcomed, especially if you have data that contradicts that...


    Steve

  9. #29
    Join Date
    Sep 2006
    Location
    Netherlands
    Posts
    1,410

    Default

    I don't have any reference to papers but I've once read that leds -such as the brake-lights of cars- are pulsed to achieve a better perceived brightness.
    There are certain duty-cycle/frequency combos that are perceived brighter then equivalent CW sources by the human eye.
    It's a common trick to lower the scanrate to enhance visibility of beamshows.

    Also at the perimeter of our eyesight we are even more sensitive to pulsing and moving light-sources.

  10. #30
    Join Date
    Jun 2007
    Posts
    99

    Default

    Yes the pulsed vs perceived brightness factor is well known, but it's just a trick on the human eye.

    The total light energy over time is the same when you run them in pulsed mode at higher current vs constant output at typical current.

    However the instantaneous light output is much higher for the time the led is on.
    Since this thread is about using LED vs Xenon to make a short flash of light the current can be set higher than for continuous operation to obtained a brighter pulse of light.

    I know they are doing something like this for cellphone cameras.
    The Nokia N900 LED flash can be driven much brighter when you use it in "FLASH" mode rather than "TORCH" mode.

    http://wiki.maemo.org/N900_Hardware_Flash_Torch

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •