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7332Re: Yet another Lightbox question

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  • jilouus
    Apr 17, 2002
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      I placed eight white leds around the opening of the box, recessed into
      3" long plastic tubes so that the light is reflected off of the back
      of the box through the difusion screens. The leds were placed so that
      there was one in each of the four corners and one in the middle of
      each flat side. They are powered with a 9 volt flat pack battery so I
      don't have to worry about another cord. Unlike light bulbs, leds
      don't get hot and rarely ever fail.

      The leds are the Radio Shack Jumbo Superbright and are wired in
      parallel. Each led has a forward voltage of 1.85 volts and the
      forward current is 20 milliamps (0.02 amps). If you were using a 9
      volt battery, you would need a resistance of:

      R = (9 - 1.85) / (8 * 0.02)
      R = 44.6875 ohms or ~ 50 ohms

      A 50 ohm, 1/4 watt resistor will work fine and the battery will last a
      very long time. I had to place the led into tubes because they were
      reflecting off the sides of the box and causing patterns in the flats.
      If you want variable brightness, just wire a 1000 or 5000 ohm
      potentiometer in series with the LEDs and the resistor

      I used the light box design found here:
      http://www.pyros.com/astrovideos/html/build_a_light_box.html

      Have fun,
      Charlie




      --- In ccd-newastro@y..., Gene Kahn <gdkahn@p...> wrote:
      > Hi
      > I am making a light box and have not seen any information on how
      much light
      > to use.
      > I am kind of new to CCDing so forgive the question if it has been
      covered
      > many times before.
      > I have a 12" LX200 and a SBIG ST-8E. The box I am building is 16"
      square and
      > 20" deep.
      > I am using 2 layers of milky plastic. I want to use 12V to power it.
      > Anybody already done
      > this and have any good suggestions on wattage?
      >
      > Any help would be appreciated.
      > Gene Kahn
      > gdkahn@p...
      >
      >
      > [Non-text portions of this message have been removed]
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