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Re: Colors



I am sensitive to students who might be embarrased by vision problems so I
tell my class these two things:

(1) If you have a vision problem you want to share with the class I would
welcome you to share it. If you are not sure it is something worth sharing,
I would be glad to discuss this with you privately.

(2) If you have a vision problem that interferes with the completion of lab
exercises in this course, please feel free to tell me about it and we will
figure out a work-around. I will keep your problem confidential unless you
specifically tell me you would like to share it with the class.

Over the years several students have volunteered to describe what they see
in various circumstances. Most have been red/green color blind of varying
degree. The most amazing was a student with the inability to see blue.
Apparently his blue sensors were defective.

There are several ways to get at these things if students are willing to
discuss it. Here are some things I do:

(a) Put a slit in a slide projector, a diffraction grating in front of the
lens, and get a nice spectrum on the screen in a darkened classroom. Point
to various places and ask the students to describe what they see. Get
descriptions of what color they call it and how bright they think it looks
compared to other areas of the spectrum.

In the case of the blue-blind student, he said he saw nothing (i.e. black)
when I pointed to various regions in the blue area of the spectrum.

(b) Put a diffraction grating in a spectroscope and put the telescope at
various positions and ask students to describe what they see. Or, ask them
to put the cross-hair at a particular spot. Good spots are... on the right
side of the spectrum at the point where you think you don't see light any
more... repeat this on the left side... center the cross hair between the
red and green region... center the cross hair between the green and blue
region.

In the case of the blue-blind student we could determine the wavelength
where his vision quit. Of course this would probably be intensity
dependent, but with our light source and grating it was about 500 nm whereas
most students can see down to about 410 nm.

(c) Obtain some of the color-blind test patterns used by doctors and by
drivers-license examiners. These can be found in various levels of
difficulty and you can determine where you can see things others don't see
and vice versa.


As a result of these kinds of activities, it is clear to me we do not all
see the same thing even though we might call something the same name. Some
red/green color-blind persons can distinguish red and green and yellow, but
with difficulty, whereas others cannot distinguish them at all. Those who
can distinguish them have learned to call the same things red, green, yellow
that I do, but it is clear they do not have the same visual experience. For
example, even though they can identify the colors, they cannot discern some
of the color-blind test patterns that I discern.



Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817