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Thread: Permanent vertical outdoor beam?

  1. #1
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    Default Permanent vertical outdoor beam?

    Greetings all.

    I arrived at this forum from a posted link on Lasercommunity and after taking the tour was pleasantly surprised at the volume of knowledge and experience presented. I figure there are some gurus here that can answer (or point me to those who can answer) some questions I have in regards to any regulations/variances/nightmares, etc., concerning outdoor light beams as art. I am located in California, USA.

    I've been thinking about an outdoor art project that would have as part of its design a fixed vertical laser beam. No scanning, no pulsing, no movement, no deviation from the vertical, and in the class IIIb range (I'm pessimistically thinking class IV approval would be too much to ask - could I be wrong?). Just a single stationary beam rising to the zenith from sunset to sunrise, 365 days a year, from a fixed location.

    Has something like this already been done? Where do I start/who would I contact about getting a project like this permitted/approved (FAA?), or is it already a non-starter, an impossible dream?

    Sincere thanks for your input! (waits for laughter, tomatoes, jeers, razzes, etc.)
    "We can't solve problems by using the same kind of thinking we used when we created them."
    --Albert Einstein

  2. #2
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    Sure, it sounds doable, the only real problem is that it'll need to be manned with observers (to turn if off if planes approach) during operation, so it'd be a bit expensive on the manpower side. And it'll also be difficult to get approved if your site is near an airport.

    It has successfully been done, most notably the luxor in vegas used to have a similar system running for years.
    More recently, LA did some Hiro laser art stuff a few years back in the city that ran for a few weeks, but that was
    terminated horizontal beams across the river.

    I honestly don't think the laser class would make that much of a difference in obtaining the proper variance (unless you chose <IIIa) as the rules for non-terminated scanning that you have to follow don't change from IIIb to IV. I think the main difficulty would be funding the project, and if you got that cleared, then its mainly sitting with your LSO nitpicking the paperwork.

  3. #3
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    Thank you.

    Observers?

    If observers are required it would definitely be a no-go; I chose a single vertical beam, not only because of the art theme, but also in order to have the best chance at approval - a fixed vertical beam presents the least hazard to aircraft (it being impossible to get the beam into the cockpit from underneath the aircraft). The only exception I can think of would be a helicopter with a wide-view canopy, such as what the local sheriff uses. Even then the chances of an accidental intersect are small; any intentional intersect would require an effort by the pilot to get "hit", but for a permanent laser installation they and other agencies would be made aware of its location as part of the variance in any case.

    After reviewing some of the regs online I can see I have some homework ahead. :? I am within 10 nautical miles of an airport, and that doesn't help matters.
    "We can't solve problems by using the same kind of thinking we used when we created them."
    --Albert Einstein

  4. #4
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    The problem seems to be that pilots would intentionally fly straight into the beam to get a better look.

  5. #5
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    If you can live with the trade off you could use a 7k or so xenon short arc. That will make a pretty strong beam and you won't have to wory about the cdrh. You will still have to get the closest air port to sign off on it but the chances of that happening are much better than a laser.

    Take a look here.. http://www.spacecannon.it/home_ENG.htm

    These are no joke. I set a tarp on fire programming a concert with a iroes 4 8k, left it pointing stage left a little too long... oops

    Chad

  6. #6
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    Quote Originally Posted by yaddatrance
    The problem seems to be that pilots would intentionally fly straight into the beam to get a better look.
    Like moths to a flame, eh? Well, any pilot that would do that gets what they deserve with no sympathy from me! :twisted:

    An arc lamp is a good fallback option, unfortunately far too big and power hungry to incorporate in the planned artwork, and the beam quality is nowhere near the match of a laser.

    I don't need a lot of power for what I have in mind. It's not intended to be a "sky-blaster"; there just needs to be a visible beam when in the vicinity of the piece, not miles away (that would be nice though! ), and if I play with the divergence and power a bit I may be able to meet the altitude exposure limits and keep everyone happy (or not), without needing observers.

    One interesting thing I've found in the FAA regs is that the allowable power/exposure limit depends on the wavelength. A correction factor - the human color sensitivity (photopic vision) - is applied to the laser power rating for calculating the maximum exposure. Not only is this correction factor very favorable for the blue laser under consideration, blue is better for atmospheric scattering (sidelight) and visibility at night (scotopic vision).

    For example, a 100mW 473nm laser with 1mrad divergence exceeds the maximum permissible exposure - inside the Critical Zone (within 10 nautical miles of an airport) - only below an altitude of 1950 feet. Doubling the divergence cuts this to 975 feet without compromising the desired effect. I've seen some indications that there is a minimum altitude above ground level at which aircraft are allowed to fly, and if I can stay under that, maybe it'll work.
    "We can't solve problems by using the same kind of thinking we used when we created them."
    --Albert Einstein

  7. #7
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    You may have some altitude restrictions for airplanes, but you also have to consider helicopters, especially the police and EMS ones. These can be flying at any altitude, and usually very close o the ground. But, in general, I'd say 500ft is a good target for your calculations.

    I think airplanes are restricted to 1000ft AGL when over a city, and 2000ft over mountains (if memory serves me well). But, again, there are other considerations. If the airplanes are approaching an airport, they can, and will, get lower as you get closer to the airport (they have to land or take off, right?).

    If you're around 10NM from the airport, and depending on the airport, airplanes should be around 1500-2500ft AGL, at least if they're on the instrument approach :roll:

    What airport are you close to?, if you don't mind my asking, that is

    All in all, if you shoot for a 500ft target, you *may* have no problems with the FAA. MAY being the operative word. However, that target may induce a high divergence. Also, you state blue is a better choice for atmospheric scattering, but I think green would be a better choice, seeing as we're a lot more sensitive to 532nm than 573nm. You may get away with a lot less power from green than using blue. Blue is nicer, though

    Any way, just my 2 cents
    Remember the future?, That'd today, as you imagined it yesterday.

  8. #8
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    Thanks for your thoughts!

    (For want of a nail the kingdom was lost. For want of a mile the variance was denied? )

    The "project" would be located nine nautical miles from Meadows Field airport in Kern County, California - just inside the ten-mile radius. Being that far away might help.

    Helicopters would probably be the only concern - there is a sheriff patrol helicopter that flies all over the city, and you are right that they sometimes fly lower than 1,000 feet AGL. They would be informed about the laser beforehand, of course, so I don't think that would be problematic if it had FAA blessing beforehand. The medical helis I've seen in the vicinity are at higher altitudes (both make a lot of noise... hmm, maybe I can demand they apply to me for a noise variance! j/k )

    As the wavelength approaches 556nm, the power has to drop significantly, as the visual correction factor goes from 0.1391 for 473nm, to 0.9524 for 532nm green. (!) In my above example that would equate to only 15mW of green! Green is much more visible in color vision, but not as much in night vision, where I expect the blue to give me an edge in sidelight visibility because of the increased atmospheric scattering, increased scotopic vision sensitivity at that wavelength, and more allowable power. The regs are only concerned with color vision because that's what would come into play in a laser-to-the-eye-in-a-cockpit scenario.

    As long as the divergence does not overcome perspective convergence the effect should not suffer. I'll have to do more research/playing with the numbers to see how much divergence I can get away with adding to the mix.
    "We can't solve problems by using the same kind of thinking we used when we created them."
    --Albert Einstein

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