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Thread: lasers or spotlights for colored "sky lights" (project)

  1. #1
    Join Date
    Oct 2016
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    209

    Default lasers or spotlights for colored "sky lights" (project)

    Mayor approved a project where we will shine few colored beams from a tower across our small town, we also got permission from the civil and military aviation bodies.
    Right now the light source is an array of high power red, green and blue laser diodes. They are not scanned, but static beams so beam diameter and distance between each other is not as big of a deal as they will diverge into each other anyway.

    My question is, is lasers perhaps not the best technology for this after all? Should we be maybe using poweful spotlights with filters? In my experience they can't be focused enough as lasers to be noticeable after 10 km (which is the goal) and lose too much brightness from filters but I might be wrong.

    What do you think?

  2. #2
    Join Date
    Dec 2007
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    Denmark
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    Default

    what power and divergence do you have from each color on the lasers now ? 10 Km is quite a long distance.

  3. #3
    Join Date
    Oct 2016
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    Default

    When I said right now what the light source is what I meant was it's how the design is on papers right now.
    And I should have provided some more info:
    1. Almost all streetlights are turned off every day at 11:00 pm. The tower itself is covered with LEDs and is turned on from 9 to 11 pm depending on the season. So overall the town and sky gets pretty dark.
    2. The tower is at one end of the town, facing the town, so many of the people in the town will be seeing the beams more coming towards them, not passing by. I've noticed this with regular laser projectors too, looking from the side the beams appear pretty dim but when you face it and the beam goes above your head it appears much brighter.
    3. Goal is 10km but 90% of the populated area is max 6 km away from the radio tower.
    4. Currently thinking about using these diodes: NUBM07 outputting 3W, NUGM01 at 1W, ML501P73 at 1W. Quantity of each depends on how much will be needed to produce a visible beam.

  4. #4
    Join Date
    Apr 2007
    Location
    Costa Rica
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    523

    Default

    I think you would need at least 20W of green to be visible for 10km - depending on atmospheric conditions and beam angle above the horizon.

  5. #5
    Join Date
    Oct 2016
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    209

    Default

    Well, let's first get one thing clear: is a spotlight an option for such distances (6-10 km) or is lasers the only practical option? I'm not aware of such spotlights for sale but maybe because there is very little demand for them rather than a limit imposed by physics.

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