Art vs Science Colors
Can you please explain (in middle school terms) why in TV
red, blue, and green light are considered primary colors and when mixed
create white light while in art, the primary colors are red, blue, and
yellow and when mixed don't come close to white. If fact if mixing red,
blue, and green paint I wouldn't get white either. Why is that?
Pigments absorb light, reflecting only the color that you see. For example,
when you mix blue and yellow pigments together, you are mixing together
compounds that absorb blue light (leaving yellow and red, which basically
looks like yellow) and that absorb red (leaving blue). The combination
absorbs both blue and red, (that's both ends of the spectrum), leaving only
green (middle of the spectrum) to be reflected. When you combine blue and
yellow lights, you see both the blue and the yellow, which is composed of
different wavelengths than the color reflected from the mixed pigments.
Color perception is kind of a funny thing; what actually happens is that
cone cells in our retinas are sensitive to different ranges of wavelengths:
basically, red (long wavelengths), green (middle), and blue (short
wavelengths). Their sensitive regions overlap a little, and your brain
processes the inputs from the different sensors to reconstruct about what
the color must be. So, if you see a monochromatic light that's in the
region two types of cones respond to, you see it as one color. Yellow
light, for instance, excites both red- and green-sensitive cones. Mixing
together monochromatic red and monochromatic green light will ALSO excite
both the red and green cones, and your brain will see yellow. As far as it
knows, it's the same color as the monochromatic yellow, but a spectrometer
could easily tell the difference.
Richard Barrans, Ph.D.
PG Research Foundation, Darien, IL
The main difference is that TV's, Computer screens, that have Red, Green,
Blue, as their primary colors give off light. In a dark room, you can still
see if a TV or computer is on because the screen gives off light, like a
light bulb. In fact, the screen is made up of thousands of tiny red, green,
and blue lights that are so close together you can hardly see them. By
turning on a Red, Green, and Blue lights that are really close, the TV can
mix the lights and create all kinds of different colors. To figure out what
colors to make, TVs start with black, and begin turning on lights, or adding
colors to get what they want.
The main point is that the Red, Green, and Blue colors a TV uses, produce
light and make colors by adding colors to the light we see.
With art, it is just the opposite. Paper and paint reflect light. White
paper reflects all the light that shines on it pretty much the same. But
colored paints do not do this, they reflect some colors better than others,
and absorb the rest. Black paint reflects hardly any light and absorbs all
colors pretty much the same. Red paint absorbs all colors but red light, and
reflects just red light. Yellow paint absorbs everything but yellow, and so
on. So when you mix two colors, you are deciding which colors to remove
from the light we see. Paint basically subtract light. Red paint subtracts
(or doesn't reflect Green and Blue). Yellow subtracts Blue, and, Blue
subtracts Green and Red. Computer printers use this kind of system where
they use Cyan, Yellow, and Magenta, which are the exact opposites of the
Red, Green, and Blue that TVs use. Cyan subtracts Red, Yellow subtracts
Blue, and Magenta subtracts Green. So, in art, you start with a with piece
of paper or canvas (this is why colors sometimes look different when you use
colored paper) and start removing or subtracting light to get the color you
want. This is why if you mix a lot of different colors together it keeps
So, the main point with paints is that paints make colors by only reflecting
some light and removing (or subtracting) the rest.
Thanks, I hope this helps.
I do not have a huge amount of time to answer this in detail. If my
schedule frees up a bit, I will give a longer answer. You have hit on a
common misconception. In color addition, the primary colors are red,
green, and blue. This is how a color monitor works. If you are looking at
color subtraction, as in the printing process, the primary colors are
yellow, magenta, and cyan. I would suggest you read the following sources:
Paul Hewitt, Conceptual Physics, 8th edition, Addison Wesley, 1998, chapter 26
There was an article in The Physics Teacher in the April 1999 that
addressed this also, but I do not have the exact cite. This is a monthly
magazine put out by the American Association of Physics Teachers, and you
may be able to search for it on the web.
---Nathan A. Unterman
I wrote an article entitled "Confusing Color Concepts Clarified" about this
that was published in The Physics Teacher magazine in April 1999, pp.
In a simple model, the color that you see depends on the "color" of light
that enters your eye. When red light and green light and blue light enter
your eye, your brain interprets the resultant color as white.
In art, the primary colors are stated to be red, yellow, and blue.
However, this is incorrect. The correct primary colors are cyan, magenta,
and yellow, just as in color printing. If you paint, you will find that
using cyan, magenta, and yellow paints can produce many more colors than
using red, yellow, and blue paints. Try it and see.
The paints absorb certain colors: cyan paint absorbs red light, magenta
paint absorbs green light, and yellow paint absorbs blue light. Paints are
always painted on a white background which reflects all colors of light.
So if you have cyan paint on top of magenta paint on top of yellow paint,
here is what happens: The white light (composed of red, green and blue
light) enters the cyan paint. The cyan paint absorbs the red light leaving
green and blue light. The green and blue light then enters the magenta
paint which absorbs the green light leaving blue light. The blue light
then enters the yellow paint which absorbs the blue light. The remaining
light then reflects off the white paper, passes through all the layers of
paint again, and then enters your eye. But since the paints absorbed all
of the incoming light, there is no light left to enter your eye. So mixing
cyan, magenta, and yellow paints results in a black color.
Dr. Lawrence D. Woolf
3550 General Atomics Court; P. O. Box 85608
Mail Stop 15/242
San Diego CA 92121-1194
General Atomics: www.ga.com/
GA Sciences Education Foundation: www.sci-ed-ga.org
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Update: June 2012