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Thread: Why can't other light sources be used to get tight (laser like) beams?

  1. #21
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    From the audience point of view, and especially indoors the laser is going to be more exquisite. A beam that is below the resolution limit of the eye is not going to be achievable with an incoherent, or I should say, un-amplified source. Outdoors, where the power needs to be in the 10's of watts and above, lasers, especially Q switched ones are very dangerous and pretty rare. Here an arc has the benefit of really high power as well as safety. The conversion from watts to visual lumens at the eye's peak sensitivity of 555nm is approximately 1 watt = 1,500 lumens. Balanced white with a CRI of 100 (sunlight) is approximately 1 watt = 670 lumens.

    P.S. That is not an honest image of 1 Watt. Either it is a composite immage or that is closer to 50 watts.

  2. #22
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    I haven't had time to read all these posts but it looks like a comparison of a non-coherent light source to a coherent light source (laser) .. there is no comparison. The laser will stay a "beam" much tighter and farther than an incoherent light source due the properties of coherent light. The Fabry-Perot dual mirror resonator cavity design in a laser allows all of the photons to be "in step" or synchronized with each other, which allows a laser to do what it does; not disperse the light quickly (colliding photons) and maintain a beam (synchronized photons) .
    Last edited by steve-o; 03-30-2015 at 20:53.

  3. #23
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    The peak sensitivity of the eye ( at high light levels as in a beam and for color), is 555nm. This is a yellow-green color.
    From experience the beam looks to me to be around 50 watts. However, 15 watts is not much dimmer because visual brightness is not linear with power. The conditions for the images are probably not identical. Sky brightness and camera settings such as exposure duration can be more significan than the power differences.

  4. #24
    mixedgas's Avatar
    mixedgas is offline Creaky Old Award Winning Bastard Technologist
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    You have to find at least TWO wavelength charts, one for photopic and one for scotopic vision. Mesotopic too if your anal.

    Steve
    Qui habet Christos, habet Vitam!
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    When I still could have...

  5. #25
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    I wouldn't persist with "this guy". That is not a 1W laser. Nevertheless, what are you trying to learn? You do not want to produce a beam of that brightness, un-terminated into the sky without a lot of safety measures.

    Outdoor projection is more demanding because the scale is so much larger and the light level is uncontrollable. You are about right about the ratios, but when trying to combine these to produce white you need to mix them in closer to 1:1:1 ratios. The sun is a black body and radiates thermally and so the peak of the energy it outputs is close to 555nm. Our eyes evolved to see best this wavelength.
    http://research.ng-london.org.uk/sci...page=blackbody

  6. #26
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    See this wiki http://en.wikipedia.org/wiki/Rayleigh_scattering describes why some colors appear brighter in the atmosphere.

  7. #27
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    Since search lights where brought up, this one was mine until some #$%^ stole it from my house it's a 75 watt short arc xenon, peakbeam systems, maxabeam is the make, ai the time they where allmost 1 grand
    Click image for larger version. 

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    Click image for larger version. 

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    this one is a light i built my self from an Australia brand, blitz light force that i put a 35 watt xenon hid lamp in, the lamp is a DS2 used on cars
    Click image for larger version. 

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    I did need to use about a one second shutter time. but it shows the difference you can do with a very small arc and a good reflector, the maxa beam has a motor controlled system to move the arc lamp to make for a tight beam or a flood,

    I did not use photoshop for these pictures, they where taken on an Olympus C2100
    Polk SDA SRS, Parasound HCA 3500, Luxman M117, Onkyo 504, 7.62X39, sometimes a ball on a string is the greatest of toys for us nonhuman types. oh and some lasers, lots of lasers

  8. #28
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    Quote Originally Posted by mixedgas View Post
    Off topic a bit.

    If I really wanted to make an Emulator or Pin Spot, I'd use what they replaced the 650 Watt Xenon with in later models. A 175 or 400 watt Cermax Xenon lamp with integral reflector. I'm really fond of Cermax sources and their Ushio and GE clones. If you buy one, get the parabolic reflector, the ellipticals will work, but the parabolic has the best collimation.

    Once I had two 1000 watt parabolic Cermax's for a project, and wow, what brightness!

    Steve
    I have the lamp section out of a runco projector that has the 1000W ballast and the xenon lamp fixture that uses the cermax internal reflector lamps. Stupid bright... Don't have a clue what I am going to do with it.

  9. #29
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    Here is what I am thinking. Take three large led arrays RGB focus light into larger diameter fiber and then collimate .

  10. #30
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    You will not be able to focus a large LED array into any kind of glass cylinder as small as a fiber. The best you can do with such an extended source is to image it with a short FL lens. The shorter the FL the smaller (tighter) the focus, but also the more divergent and there is a limit on how divergent the rays can become before they will fail to be contained in the "fiber" by total internal reflection.

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