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Thread: crowd scanning reduex.

  1. #1
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    Default crowd scanning reduex.

    i've read a fair amount of posts concerning crowd scanning here and,even being from the u.s where it is pretty much forbidden,i know it can be done responsibly.
    i read one post refering to having seen crowd scanning done w/ 40w lasers.
    this video shows a really nice looking six watt system.
    http://video.google.com/videoplay?do...arch&plindex=5
    even if i were operating in unregulated lands i would pause at this level of crowd exposure.

  2. #2
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    Cool

    I wouldn't want to be the guy running the lasers at that show - at least not here in the US!

    It's difficult to judge exposure from a video, especially when there are so few lights in the scene. (It looks mighty dark in there, so in theory they could have had the laser power turned down and it still would have looked bright.)

    But even so, my experience tells me that the beams in that show couldn't possibly be weak enough to pass muster with the CDRH. The beams simply don't diverge enough. I'll bet that they were *way* above the PEL with most, if not all, of the effects shown in that video.

    Granted, the CDRH regs are quite conservative, as there are shows that you can do legally in the UK that you can't do here. But even so, they *are* the law here, and I don't see how you'd ever get away with a show like that here in the US.

    Adam

  3. #3
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    Lightbulb

    That looked awesome, but I would not want to hang out behind that thing... It looked very unsafe to my inexperienced eyes... I would have asked for goggles at the door.
    Love, peace, and grease,

    allthat... aka: aaron@pangolin

  4. #4
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    Default

    *shrugs*

    can't say for sure how divergent those beams were - that was a pretty big room.
    Now proudly stocking and offering the best deals on laser-wave

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  5. #5
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    Default

    And the beams are moving very fastly...

  6. #6
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    Default

    Quote Originally Posted by sbk View Post
    And the beams are moving very fastly...

    here is some interesting info on duration of exposure...


    The duration of exposure also plays a role in eye injury. For example, if the laser is a visible wavelength (400 to 700 nm), the beam power is less than 1.0 mW and the exposure time is less than 0.25 second (the human aversion response time), no injury to the retina would be expected to result from an intrabeam exposure. Class 1, 2a and 2 lasers fall into this category and do not normally present a retinal hazard. Unfortunately, intrabeam or specular reflection viewing of Class 3a, 3b, or 4 lasers and diffuse reflections from Class 4 lasers may cause an injury before the aversion response can protect the eye.

    NOTE: Laser retinal injury can be severe because of the focal magnification (optical gain) of the eye that is approximately 105. This means that an irradiance of 1 mW/cm2 entering the eye will be effectively increased to 100 W/cm2 when it reaches the retina.

    i may be preaching to the choir but it is good to have reminders of this info.

    i have to be even more careful because one of our shows uses a 3watt pulsed laser.

    For pulsed lasers, the pulse duration also affects the potential for eye injury. Pulses less than 1 ms in duration focused on the retina can cause an acoustical transient, resulting in substantial damage and bleeding in addition to the expected thermal injury. Many pulsed lasers now have pulse duration less than 1 picosecond.

    it is hard to judge from video but like i said,it can't hurt to have this info revisited sometimes and perhaps there are folks to whom this specific info is new.

    peace,
    wes

    Last edited by wes; 07-03-2007 at 07:17.

  7. #7
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    Default

    remember, fast beams may be your worst enemy when doing audience scanning, repeat rate increases exposure. One of the neat things in my collection is a early cdrh guide on how to do the mathematics for audience scanning, most effects are low and slow, to a point. what kinda kills aud scanning in the us is if the audience is wearing glasses, and you have to assume they are, you jump from a 7 mm collection arpeture to a 50 mm one under the rules, ie optically aided collection, and your allowed power must take a dive.

    Steve

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