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Reflection of Infrared

Discussion in 'General Electronics Discussion' started by Ipduo, Jul 28, 2010.

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  1. Ipduo


    Jul 28, 2010

    I'm try to design a system to detect a white object. I'm just wondering about the reflection/absorption of IR.

    If an IR LED was shone on a darkly coloured floor or outside on grass would any IR be reflected (or sufficient to trigger an IR photodector... I could modulate it if needed). Furthermore, if I then placed a white object on the ground would this increase the reflection to a sufficient degree for a system to determine that something had been placed there. The range isn't massively important although I expect maybe about 1m distance from LED to ground / object.

    Sorry for the vagueness of this question - I'm open to suggestions / comments on this!
  2. eptheta


    Dec 20, 2009
    From my experience, the range depends on your modulation, duty cycle and well power input into the IR LEDs.
    I made an IR remote control and it could easily reflect and detect off white walls from over 5m away, but it did have trouble when it came to black surfaces............
    So far, i have only tested it on flat walls not on curved surfaces. If you would like me to test it out then go ahead and ask. If you have built your own IR transceiver module then you might as well try it yourself.
    Post back with your results
    Good luck
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Also remember that if this is in daylight, there is a large IR emitter that will tend to dwarf any locally generated source :)

    An interesting fact is that grass is actually quite a good reflector if IR. The problem is that the reflectance is diffuse.
  4. Ipduo


    Jul 28, 2010
    Thanks guys. I appreciate the sun might be a problem but if I modulated my IR source would the reflected beams be similarly modulated and thus discernable from the background IR?

    And eptheta, if you wouldn't mind just seeing if it worked on grass I've be very grateful. I haven't built one myself but don't want to waste time and money if the reflections from grass are strong, as I suspect that means detecting something on grass would therefore be difficult.

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