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Best location for a light bulb filament using a concave mirror?

  1. Jul 26, 2011 #1
    Where is the best location for a light bulb filament to be placed in a spotlight, when using a concave mirror?

    It makes the most sense to put it at the focal point of the mirror if you want parallel light beams but are you supposed to have parallel light beams when you use a spotlight? Or do you want the beams to diverge slightly so the light covers a larger area? I also read that in some slide projectors, the light bulb is placed at the center of curvature.. is this the same thing as radius of curvature? Or are they meaning focal point? I'm just a little unclear..

    Thank you in advance for your help!
  2. jcsd
  3. Jul 27, 2011 #2
  4. Jul 27, 2011 #3


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    Don't forget that no light bulb is an actual point source of light, so while some point on the filament may be exactly at the focus, the rest of is will be slightly off, giving a certain amount of spread.

  5. Jul 27, 2011 #4
    Okay, that's great, thank you to the both of you! I can put together a sufficient answer with all of that info. Thanks again.
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