Re: [Phys-l] Light mystery

["Pete Lohstreter" <plohstreter@mail.hockaday.org>]

Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu> writes:
> When I take a green laser pointer and aim it at a white paper I get a
> green
> dot and green diffuse reflection on the white wall. When I take the same
> green laser pointer and point it at fluorescent orange and/or fluorescent
> pink paper, I get a yellow spot on the paper and I still get green diffuse
> reflection. I'm guessing that I'm getting some excitation similar to when
> it
> is lit by UV light. But I don't see why I'm getting the green reflection.
> Can someone verify if my excitation idea is on track and explain the why I
> get the green reflection? It is as simple as the source is green and some
> light is absorbed while non-absorbed photons are reflected?
> Thanks in advance.

You explanation is exactly what I would expect.  Several years ago when
fluorescent papers (dyes) were becoming common, I shined an blue light
(filtered from a slide projector) onto a fluorescent orange paper and it
looked bright red.  A student asked where the red came from since the
light contained no red.  Stumped me for a while until I realized that
fluorescence did not require UV light just light with an energy high
enough to cause the fluorescent dye to glow at its designed color.

The reflection of the green light from the fibers of the paper would
certainly look green since no change is occurring to them.


Great question.  I'm going to have to try it.



Pete Lohstreter                           "Happy is he who gets to know 
The Hockaday School                 the reasons for things. "
11600 Welch Rd                          Virgil (70-19 BCE) Roman poet.
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plohstreter@mail.hockaday.org

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