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help in making infra red light!

Discussion in 'Electronic Basics' started by john Smith, Oct 3, 2005.

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  1. john Smith

    john Smith Guest

    Hello,

    I hope this is the right place to post this message as I wish to know is it
    possible to make an infra-red flood light using LEDs.

    I recently purchased what I thought was one form maplins for 60 GBP but it
    turned out to be more of a spotlight, lighting up only a small area of

    my drive., I want to know would it be possible to make a light that could
    cover a wider area using i/r led's, possibly the ones you can buy for

    maplins for a couple of pence each.

    I'm sorry if I have posted this in the wrong place, but any advice would be
    gladly received


    Thanks in advance
     
  2. It is certainly possible, but it takes a lot of LEDs, since each puts
    out only a milliwatt or so of light energy. It is often more
    practical to cover a large incandescent lamp (250 watt brood lamps,
    for example) with an IR long pass filter when a big flood is needed.
    Most theatrical color filter gels pass IR, so using a few different
    deep colors, like blue and red, block most visible, but pass IR.
    These are fairly cheap in large sizes.
     
  3. Eric R Snow

    Eric R Snow Guest

    In the 1970s, we used Kodak Wratten #87 filters, which could be bought
    in 10cm by 10cm sheets for not much money, but Kodak stopped making
    them. The story was that then new environemntal regulations had
    rendered manufacture of the necessary dye too expensive for the
    market.
    (#87 filters may be back; I haven't checked in years.)

    The alternative was actually better than Wratten #87 filters, which
    were
    expensive, fragile, and tended to bleach under the light.

    What we used instead was a tripack of ordinary theater-light filters,
    such as those made by Rosco. These filters are used in front of a
    1000-watt lamp, and only ~4% of that is visible light. Of necsssity,
    all theater-light filters pass infrared, to avoid combustion.

    So, what one does is to stack three complementary filters, such that
    all
    visible light is blocked, allowing only infrared to pass.

    What you want are generically called "plastic gels" in the stage
    lighting trade, and are made of dyed plastic film, not gelatin. The
    Rosco product is "Roscolux". <http://www.rosco.com> I don't recall
    the exact colors we used, but it wasn't hard to figure out. One just
    got (for $15) a sample book, and tried combinations out.

    There are a number of competitors as well.

    There are glass filters that pass IR and block visible, probably made
    by
    Schott and perhaps Hoya, but these were too expensive for us. Theater
    filters are something like $6 for a 20" by 24" sheet, and widely
    available.

    Joe Gwinn
     
  4. spudnuty

    spudnuty Guest

    If you call your local Rosco dealer you can get a "Roscolux" sample
    book sent to you for nothing if you are in the "trade" (wink, wink).
    The book is quite cool as each film has a graph of its transmission vrs
    wavelength. You can pick the wavelengths you want passed by stacking up
    the graphs. I made a nice homemade safelight doing this.
    Also Bill Beaty also did some cool research at:
    http://www.amasci.com/amateur/irgoggl.html
    He used: " "Congo Blue" (Lee #181, or Rosco #382) costs maybe $8 for
    24" sheet
    Optional: sheet of "Primary Red" filter gel (Lee #106 or Rosco #27)"
    and made a pair of goggles for viewing IR.
    Richard
     
  5. Rich Grise

    Rich Grise Guest

    Well, LEDs generally have a fairly narrow beam too, so you'd need a
    bunch of them in an array all aimed a little differently. And you'd
    need a bunch of them to give any reasonable level of illumination.

    Or, you could find some kind of IR transparent diffuser, like you
    see on headlights or LV yard lights, to spread out the beam, or look
    for a "full-page magnifier" (in an office-supplies store, or on-line),
    and if it's IR transparent, it should spread the beam also, albeit
    possibly not as evenly as an actual diffuser.

    Good Luck!
    Rich
     
  6. Pooh Bear

    Pooh Bear Guest

    Going back to my lighting days, I recall that deep blue filters in front of high
    wattage lamps used to 'char' from the absorbed energy !

    Graham
     
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