Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "plnelson2003 
<peter@s...>" <peter@s...> wrote:
> Peaky spectra **IS** what causes metamerism, regardless of whether 
> you're talking about inks or paint chips or geology minerals! The 
> physics and perceptual science of metamerism is not in question.


Just a followup to this for anyone with an interest in science.

Most science museums have little metamerism demo's.  The
one in Boston, for instance, has one with 2 little boxes
each lit seperately, and pile of colored chips.   The boxes
LOOK like they're lit with the same color light and if
you put your hand in it (usually) looks about the same in
both boxes.  But if you pick up a chip and put it in one
box the chip looks yellow; put it in the other and it looks
black.

You can easily make your own metamerism box to amuse yourself,
your friends and your kids.  Make two boxes and light the
inside of one with a small fluorescent tube used for a
softbox.  Go down to Radio Shack and buy red, green, and 
blue LED's (It's a good idea to buy several of each for 
more light and better diffusion.)  Light the inside of
the other box with the LEDs.  LED's have a very narrow (typically
20 degree) angle of "out"cidence so you will have to fiddle
with pointing and diffusing them to light a spot in the box
evenly.  Adjust the levels of the LEDs with resistors or extra
diffusion so they are balanced to white.

LED's have EXTREMELY narrow output spectra - just a few
nm wide!  So even though the light will look white to
your eye, the peaks will often fall totally between 
the reflectance spectra of many common dyes and pigments.

Find common household items, of different colors and place
them in the fluorescent box where they should look normal,
and then in the LED box where they will sometimes have a
dramatically different color.  It will be common to find items
which look purple in one box and blue in the other or yellow
in one and green in another, or that are a bright color in one 
and turn nearly black in the other, etc.   It's a great 
introduction to the physics and perceptual science of color
for kids and adults.