IES Calderón – Gijón
Departamento de dibujo
ART 3º ESO Bilingual Section
PHYSICS OF THE COLOR
THE ELECTROMAGNETIC SPECTRUM
The electromagnetic spectrum is more familiar to you than you might think. The microwave you
use to heat your food and the cell phones you use are part of the Electromagnetic Spectrum. The
light that our eyes can see is also part of the electromagnetic spectrum. This visible part of the
electromagnetic spectrum consists of the colors that we see in a rainbow - from reds and oranges,
through blues and purples.
Waves in the electromagnetic spectrum vary in size from very long radio waves the size of
buildings, to very short gamma-rays smaller than the size of the nucleus of an atom.
Each of these colors actually corresponds to a different wavelength of light.
Visible light waves are the only electromagnetic waves we can see. We see these waves as the
colors of the rainbow. Each color has a different wavelength. Red has the longest wavelength and
violet has the shortest wavelength. When all the waves are seen together, they make white light.
When white light shines through a prism, the white light is broken apart into the colors of the
visible light spectrum. Water vapor in the atmosphere can also break apart wavelengths creating a
See Newton experiment with a prism:
dividing light into colors.
Newton's opposite demostration: adding colors
to get white light through fast rotation of a color
Each color has a different wavelength.
HOW DO WE SEE LIGHT AND COLORS?
Cones in our eyes are receivers for these tiny visible light waves. The Sun is a natural
source for visible light waves and our eyes see the reflection of this sunlight off the
objects around us.
The color of an object that we see
is the color of light reflected. All
other colors are absorbed.
A black sweater is warmer
because absorbs all the radiations
The retina anatomy.
The retina contains three types of color receptor cells, or cones, and one type of light-sensitive
Cones are divided into three types, each one specialized in one color:
One type, relatively distinct from the other two, is most responsive to light that we perceive as
The second type is most sensitive to light we perceive as yellowish-green.
The other type is most sensitive to light perceived as green.
The other type of light-sensitive cell in the eye, the rod, has a different response curve. In normal
situations, when light is bright enough to strongly stimulate the cones, rods play virtually no role in
vision at all. On the other hand, in dim light, the cones are understimulated leaving only the
signal from the rods, resulting in a colorless response.
Whe excited by light, these cells send messages to the brain. This organ elaborates the perception of
light and colors.
SUBTRACTIVE COLOR MIXING: CMY
A subtractive color model explains the mixing of paints, dyes, inks, and natural colorants to create
a full range of colors, each caused by subtracting (that is, absorbing) some wavelengths of light and
reflecting the others. The color that a surface displays depends on which colors of the5
electromagnetic spectrum are reflected by it and therefore made visible.
ADITIVE COLOR MIXING: RGB
An additive color model involves light emitted directly from a source or illuminant of some sort.
The additive reproduction process usually uses red, green and blue light to produce the other colors.
Combining one of these additive primary colors with another in equal amounts produces the
additive secondary colors cyan, magenta, and yellow. Combining all three primary lights (colors) in
equal intensities produces white. Varying the luminosity of each light (color) eventually reveals the
full gamut of those three lights (colors).
Computer monitors and televisions use a system called optical mixing and cannot be considered
additive light because the colors do not overlap. The red green and blue pixels are side-by-side.
When a green color appears, only the green pixels light up. When a cyan color appears, both green
and blue pixels light up. When white appears all the pixels light up. Because the pixels are so small
and close together our eyes blend them together, having a similar effect as additive light. Another
common use of additive light is the projected light used in theatrical lighting (plays, concerts, circus
shows, night clubs, etc.).
Bayer pattern in a digital sensor
into a camera
CMYK PRINTING PROCESS
The CMYK color model (process color, four color) is a subtractive color model, used in color
printing, and is also used to describe the printing process itself. CMYK refers to the four inks used
in some color printing: cyan, magenta, yellow, and key black. Though it varies by print house, press
operator, press manufacturer and press run, ink is typically applied in the order of the abbreviation.
The “K” in CMYK stands for key since in four-color printing cyan, magenta, and yellow printing
plates are carefully keyed or aligned with the key of the black key plate. Some sources suggest that
the “K” in CMYK comes from the last letter in "black" and was chosen because B already means
blue. However, this explanation, though plausible and useful as a mnemonic, is incorrect.
Colors affect us in numerous ways, both mentally and physically. A strong red color has been shown
to raise the blood pressure, while a blue color has a calming effect.
THE COLOR WHEEL
A color wheel is an abstract illustrative organization of color hues around a circle, that show
relationships between primary colors, secondary colors, complementary colors, etc.
The first color wheel was designed by Sir Isaac Newton (see last page).
There are several models. Here you have some of them:
CLASSIC ARTIST RYB COLOR WHEEL AND COLOR STAR
CMY COLOR WHEEL: WE WILL USE THIS MODEL WITH OUR GOUACHES COLORS
It is the pure color, its name.
A Tint is sometimes called a Pastel. It's simply
any color with white added.
A Shade is simply any color with black added.
A Tone is created by adding both White and
Black. Any color that is "greyed down" is
considered a Tone.
Shade, tint and tone are terms that refer to a variation of a hue.
Chroma: How pure a hue is in relation to gray.
Saturation: The degree of purity of a hue.
Intensity: The brightness or dullness of a hue. One may lower the intensity by adding white or
Luminance / Value: A measure of the amount of light reflected from a hue. Those hues with a high
content of white have a higher luminance or value.
Colors at their basic essence;
those colors that cannot be
created by mixing others.
In subtractive mixing, primary
colors are: CIAN, MAGENTA
and YELLOW (CMY)
In aditive mixing, primary
colors are: RED, GREEn and
Those colors achieved by a
mixture of two primaries.
Primary in one mixing are
secondary in the other!
Those colors achieved by a
mixture of primary and
Those colors located opposite each other on a
Those colors located close together on a color