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Re: TV remote control LEDs wavelength?

Discussion in 'Lighting' started by Don Klipstein, Aug 10, 2006.

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  1. These sure appear to me (in my experience) to be GaAs LEDs - usually
    completely invisible in a dark room to most human eyes even when dark
    adapted. I have seen some GaAs LEDs glowing barely in conditions
    favorable for me to see them, but I usually find their output to be
    completely invisible.

    The peak wavelength of those is usually 940 nm.

    There are GaAlAs infrared LEDs with peak wavelength usually 880 nm, at
    least usually the nominal peak wavelength is. I usually find these to
    slightly visibly glow when I look into them when they are operating.

    I avoid staring into operating IR LEDs for more than a few seconds
    unless I know that I am not going to exceed or get close to any limits of
    21 CFR 1040.10, which actually does not have regulatory force over LEDs
    anyway but on lasers. However, it does appear to me that TV remotes are
    reasonably safe products.

    - Don Klipstein ()
     
  2. JohnR66

    JohnR66 Guest

    I tried two cameras and they both respond. Oddly, one is purpleish and one
    makes it appear like a blue LED. Overall not very strong due to the camera's
    IR filter. With a B&W video camera, response was quite strong that I can
    point the remote at a wall several feet away and see the circle of light
    produced. Most digital cameras have an IR filter built in. A few older
    models had a weak or no filter and using an IR pass/visible light blocking
    filter would produce some cool effects like white grass and trees.
    John
     
  3. Another LED nut, Craig Johnson (LED Museum), has a web page on infrared
    LEDs, including some photos taken with digital cameras. He shows several
    diferent wavelengths of IR LEDs, and the funny colors they appear to the
    digital cameras that he used.

    http://ledmuseum.home.att.net/ledir.htm

    It turns out, my digital camera has enough sensitivity to IR to render
    off-color (magenta-ish) glowing coals in a fireplace!

    - Don Klipstein ()
     
  4. Travis Evans

    Travis Evans Guest

    This is quite fascinating. I discovered several years ago that IR LEDs
    in remote controls could be "seen" by our camcorders. Our current one
    is especially sensitive when switched into "NightShot" mode, because
    that's how it's designed--it uses IR LEDs which are mainly invisible
    (except for the dim red glow I notice when they're on that I don't see
    with ordinary remote LEDs) to allows shooting (black-and-white) images
    even in complete darkness.

    I've had interesting results looking at ordinary objects with NightShot
    mode turned on. I assume that NightShot mode switches it into a
    special mode where it effectively becomes an IR camera. The most
    obvious is that red and white objects look nearly the same shade, so
    red text on a white background (or vice-versa) become nearly invisible,
    which makes sense because IR is close to red in the spectrum. I've
    found some objects that appear dark in visible light but look very
    bright with NightShot on. I've seen a dim gray background on the
    vacuum-fluorescent display of a stereo system we had in the past that
    didn't show up to my eyes (probably produced by the IR of the heating
    filaments?). Before looking at the IR filter on a remote control, I
    guessed that it would look clear in this mode since I knew the filter
    was designed to block most visible light but pass IR, and I was
    right--I turned on NightShot mode while looking through the viewfinder,
    and I could instantly see right through all of these filters as if they
    were crystal-clear.
    Last Independence Day I noticed something odd like this--a firework that
    had just gone out seemed fuzzy and looked as if it was glowing a very
    odd dim white color when I looked at it through the viewfinder (I was
    not in NightShot mode, just ordinary visible-light color mode), and I
    didn't see this color through my other eye which was not looking
    through the viewfinder. It must have been the IR emitted by it.
     
  5. David Lee

    David Lee Guest

    Travis Evans wrote...
    Actually it's the opposite way around. All CCD cameras are sensitive to IR
    and a conventional camera includes a filter to eliminate the effects of IR
    radiation. A camera with "NightShot" mode simply has the facility to switch
    out this filter - so it is an option with almost zero cost to the
    manufacturer.

    David
     
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