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Project sharp shadows from LED

  1. Nov 30, 2015 #1
    Using a high-power LED light (the surface mount kind, about 4x4mm with 120 degree viewing angle) I'd like to project shadows of a fine metal mesh onto a wall.

    I have tried various lens arrangements and found that placing a pinhole in front of the LED makes the sharpest shadows. This makes sense, because the LED has an 'aperture' that is 4x4mm, so the shadows have some blur. Making the aperture smaller makes the shadows sharper.

    I was wondering if it's possible to focus the 4x4mm LED aperture to approximate a point source. Wouldn't collimating the LED light, then passing it through a convex lens cause the light to focus at one point, effectively making a point source? I have tried many different lens configurations to attempt to achieve this, but none have been successful. All of my attempts result in a projection of the LED die.
    Any help or insight is much appreciated!
  2. jcsd
  3. Dec 1, 2015 #2

    Andy Resnick

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    LEDs are extended sources; the procedure you describe (focus the light onto a pinhole) is called 'spatial filtering' and will indeed help. It's important to use a pinhole aperture, tho.
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