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Infrared laser - remote control

  1. Jun 13, 2009 #1
    Hey guys, I'm not exactly sure on which forum I should be posting this topic but I decided to post it here. Any mod can move it if deemed necessary.

    Anyway, I have been wondering about the infrared wavelengths that a remote control emits when trying to control, say, a TV or VCR/DVD player

    I read that the infrared wavelength must follow line-of-sight to the infrared receiver in the device that is being controlled. For example, a infrared laser cannot travel around corners. However, if I point my remote control in the opposite direction, facing my black couch, the device can still be controlled. Is this because of some kind of "bouncing-off" effect? Can someone explain the physics of what is going on?

    Also, if a panel of glass is placed over the infrared receiver, will it still pick up the remote control signals? What about paper? What about a tank of water?

    The reason I am asking is because I am interested in how infrared wavelengths can be applied and I don't have the means to actually perform these experiments.

    If anybody can shine any light on this subject, it would be greatly appreciated. Thank you.
  2. jcsd
  3. Jun 14, 2009 #2


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    Staff: Mentor

    These devices use omnidirectional infrared emitters, not lasers. My DVR has an issue where random IR from my LCD TV emitted into the room overwealms the receiver, making it miss signals from the remote. A piece of paper taped over the receiver blocks enough of this ambient IR that the remote can function.

    This isn't S&D material, though...
  4. Jun 15, 2009 #3


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    Science Advisor
    Gold Member

    If you have a camera or camcorder with an IR mode you can use it to see what your IR receiver sees. The IR signals indeed bounce off walls and furniture, just as if you were shining a flash light.
  5. Jun 15, 2009 #4


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    Science Advisor

    As an exercise, you might try putting different things against the back of your couch. Some examples that come immediately to mind would be a T shirt, an unfinished board (like a piece of plywood), a finished board (like a folding table or something), a paper towel, etc..

    If you get the same results every time, you can conclude that your device is seeing infrared light directly from the omnidirectional bulb. If you get variation on the results, then at least part of the signal your device is receiving being transmitted by reflection.
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