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Break white light into it's components

  1. Dec 9, 2009 #1

    I need to make a demonstration that shows that white light is composed of different colors. I do not have a prism, and will not be able to obtain one in time. I have a white LED flash light, and I tried some improvisations with different objects (bottles, glasses etc), but none seems to decompose the white light. This led me into thinking, is light produced by white LED somehow different from the ordinary white light?
    Maybe you can think of some other improvisation that demonstrates the effect I need?

    Thank you for the help.
  2. jcsd
  3. Dec 9, 2009 #2


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    Staff: Mentor

    Yes, the light spectrum of a white LED is different from the spectrum of an incandescent bulb. You should be able to find the LED spectrum in its datasheet, and the spectrum of an incandescent bulb from a google (images) search.

    Even though you don't have a "prisim", do you have access to any blocks of plastic or glass? Even a square drinking glass can be made to split out the spectral components for you. Or use a slit on top of a pan of water, and shine the light in at an angle...

    Or as you suggest, shine the white light through various transparent colored materials, and show that the original light had some of that color in it...
  4. Dec 9, 2009 #3


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    Homework Helper

    Most (all?) white LED's are composed of a red, a blue, and a green LED that, when combined, give white light. Remember that LED's work when electrons recombine with holes and give off photons with the same energy as the semiconductor's energy gap. That means all "pure" LEDs give off a single wavelength of light.

    If you want to split light, why not use a CD? I've used it to look at LEDs, fluorescent lamps, incandescent bulbs, and even the spectral absorption lines of the Sun. It works quite well.
  5. Dec 9, 2009 #4


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    Staff: Mentor

    Hah! Very cool idea.
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