Please note I am not talking about narrow bandwidth definitions. I am
talking about objects in everyday life, and I am talking about
broad-band colored gelatins or similar filters. Also note that I
realize the public definition of blue is spoken/intended way more often
than a more scientific definition of blue.
Having noted those things, please do or imagine the following
experiment/demonstration...
Project a visible spectrum on a white dry-erase board in a semi-dark
room. Ideally this should be bright and a couple feet wide. Ask an
individual or group to identify the blue region of the spectrum. Have
them use a marker to draw boundaries on each end of the region they
consider blue. You can allow them to draw the boundary as a wide region
that you can call the "transition zone." On the short-wavelength side
of the transition zone you want the group to agree the color is blue.
On the long-wavelength side of the transition zone you want the group to
agree the color is green.
Do the same boundary/transition zone for green turning to red.
End up with a blue region, a green region, and a red region that eveyone
can pretty much agree with, as well as the transition regions between
them. Minor border disputes are okay and point out differences in
perception and opinion. For what follows, border disputes won't matter.
It is my experience with many students over many years that the center
of the transition between blue and green will be about 495 nm. The
width of the transition might be as narrow as 480 to 510 or as wide as
470 to 520. In other words, a typical group of people will say that 480
and below is clearly blue while 510 and above is clearly green.
Students might identify the transition as blue-green.
The center of the green/red boundary is easier to agree upon; it is
quite near 590 nm and is universally identified as yellow. The width of
the green red transition might run from about 570 to 620. The problem
at the low end is deciding when to call it green as opposed to something
like lime-green. The problem at the high end is deciding when to call
it red as opposed to orange.
Turn on the lights and take a filter that looks about the same as the
cyan ink on an inkjet printer. I have Rosco theatrical filters. I have
a particular set that is good for demonstrating blue, cyan, green,
yellow, red, magenta. I got my choice from a Physics Teacher article
published about 25 years ago. I can supply the Rosco numbers, except
not right now because I am typing from home.
Anyway, I pick out the filter I call cyan, and I ask the group to tell
me what color it is. Almost every person calls it blue. Only an
occasional person calls it cyan or blue-green. Many comment it is a
very pretty blue or even that it is their favorite color of blue.
Darken the room and put the cyan filter between the light source and the
maker board, or give each person a small piece they can look through.
The filter I use transmits all the way from the blue/UV boundary clear
up to the bottom of the transition between green and red. In other
words, it totally encompasses the region they already identified as
green in addition to the region they identified as blue. In terms of
their previous agreement on what is blue and what is green, it is
clearly just as proper to call this filter green as to call it blue.
The participants readily agree this is true, yet most claim they will
continue to call it blue. I suggest maybe they should call it cyan.
Some will and some won't.
Hopefully someone will ask if I have a filter that transmits blue only.
As a matter of fact I do. With the room still darkened, I pass it out.
Even this filter has a trace of green leaking though, but nothing like
the previous one. Everyone will agree that this is a better example of
blue than the first filter, based upon what portion of the spectrum it
transmits.
When I turn on the lights they see the blue filter I just gave them is
quite dark blue. Some will say it is violet, even though they just
observed it transmits light all the way from about 400 to 510 (the
previously-identified blue region PLUS the blue-green transition
region). Yet, some are reluctant to call it blue, preferring to call it
dark blue or violet. Some still think (more from their feelings than
from their intellect) the cyan filter is the better blue, even though
the demo showed it clearly is not.
* * * My point is... * * *
I am not only talking about a conflict between a physics definition of
color and a public definition of color. Right now I am talking about an
inconsistency totally within public perception. The spectral regions
reflected/transmitted by objects people call blue do not match the
portion of the spectrum these same people identify as the blue region of
the spectrum. That doesn't always convince them to call it cyan, but
they at least realize there is just as much green light coming from that
object as there is blue light. There is no doubt about this, and they
all agree. They saw it with their own eyes, but they don't necessarily
agree to change what they call it.
Although I agree with Denker that I am not likely to go into a fabric
store and ask for cyan, I do eventually get around to that. I might
say, "I am looking for a blue-green color. Actually, what I am looking
for is cyan. Do you know what cyan is?" If so, great. If not, I ask
them to show me the light blues or the blue-greens, or the turquoise or
teal. If I find what I want, I will likely say, "To my eye, this is
cyan. Cyan is mixture of blue and green. That's what I think this is."
I figure it doesn't hurt to spread the word, even though it is likely
the clerks are rolling their eyes as I walk away with my purchase.
We actually have a nice quilting and fabric store here in Bluffton. I
go there with my wife (who quilts) to help her choose fabric. I think
my wife views these excursions as entertainment with a bit of education
and a bit of embarrassment, and she sometimes joins the clerks with the
rolling of the eyes. Yet, she keeps asking for my opinion on what
colors to choose, and the quilts and wall hangings are beautiful.
Michael D. Edmiston, Ph.D.
Professor of Physics and Chemistry
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu
_______________________________________________
Phys-L mailing list
Phys-L@electron.physics.buffalo.edu https://www.physics.buffalo.edu/mailman/listinfo/phys-l