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How do these straight line lasers work?

  1. Nov 11, 2004 #1
    I am not sure what the thing is actually called, but let me see if I can describe it. It is one of those products advertised on tv, that you put on a wall and it shoots a laser beam all along the surface parallel with the ground.

    The problem I can't figure out is, some of them claim it can go around corners (i.e. around a corner onto a wall the device can't even see directly).

    It seems like this should be impossible to me, and I can't figure out how it would work. Anyone have any idea?

  2. jcsd
  3. Nov 11, 2004 #2


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    Light can go around a corner if you use a mirror! :-)
  4. Nov 11, 2004 #3
    Haha, of course...but they don't claim to use any mirror in this commercial.

  5. Nov 11, 2004 #4
    Light can go around a corner to a small degree by diffraction, but in your case I doubt this is so, because from what you described, it sounds like the laser has to make a 90° turn. I don't know what this advertisement is trying to sell, but if it's something like a detector, then it could be possible that this laser can go through walls.
  6. Nov 11, 2004 #5


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    It's called the Laser Straight, and you can Google it. I found this: http://www.asseenontv.com/prod-pages/laser_straight.html?gid=

    As for the "going around corners" mystery, it's a "think outside the box" problem. What does it mean to go around a corner? We *assume* that the device is attached to the same wall that has the corner.

    No, the laser is not the trick, the placement is the trick - just attach it to a wall *opposite* your corner, and point it strategically. It shines across everything - inner corners as well as outer corners!

    Look at the images here: http://www.surftilyoudrop.com/laser-straight.htm
  7. Nov 11, 2004 #6
    Yes, it appears from those pictures that the laser comes out as a straight line rather than a single spot. That is, if you shine it on the wall, it looks like:
    rather than

    Thus, if you put it on the opposite wall, it will illuminate all corners.
  8. Nov 11, 2004 #7

    Well that makes perfect sense..though I really could have sworn they had it placed on the same wall it was going around, in the commercial. Maybe they really didn't have it attached and the guy was just holding it, to kind of trick the audience...though I don't see why they would do that.

    Either way, its a neat little gadget :)

    Thanks for the googling.

  9. Nov 11, 2004 #8


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    My first thought is that the beam is scanned. They are moving it rapidly back and forth across the wall. You would see only a spot, if it held still long enough.

    The scanning would also enable them to have a bit more powerful beam, and remain safe. Should you happen to look into the device, since the beam is continuously moving, it will not be in one place long enough to instantly damage your eyes.

    I would not recommend staring into the beam irregardless.
  10. Nov 14, 2004 #9
    I have used laser levels for preparing the ground prior to concrete work. I would imagine the ones used indoors work the same way. They basically have a laser shooting straight up or down and a revolving mirror to make a complete 360 degree sweep. It is entirely possible that the indoor lasers work the same way. You may have seen it placed next to a wall in the commercial and noticed the beam on that wall. Then the next scene showed a corner on an opposite wall and what do you know, there is a line going around the corner. Advertising gimmick. Although technically not dishonest, it is somewhat misleading. Incidentally, they work quite well. Speeds up dirt work incredibly.
  11. Nov 16, 2004 #10
    Even if this model doesn't sweep 360 degrees it can still project around a corner (just not very far). If the beamlet sweeps let say 5 degrees and you place it flat on a wall 10 feet from the corner, the beam project along the wall the device is on the 10 feet to the corner and around the corner about 10.5 inches. They could have it sweep any angle they wanted. 5 degrees was just for the sake of example.
  12. Nov 16, 2004 #11
    Macgyver I don't understand what you are talking about. Laser beams travel in straight lines. At least for the purpose of THIS discussion. As someone has already said, it is all in placement. My main point is that the laser is placed so that it sweeps across an opposing corner.
  13. Nov 16, 2004 #12
    Sorry Averagesupernova, I wasn’t very clear. I was just pointing out that you can have a wide angle projection (project a line) that does not emanate 360 degrees around the source. You can use a spinning mirror or a refractive lens to produce a projected arc that is smaller than the arc of the 360 degree devices you were referring to. This is how the devices advertised on TV can do what they show. I don’t believe it to be misleading advertising.

    But I suppose I am just disputing details and repeating what others already said. That’s my fault for just skimming through what was posted.
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