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Color and Vision
The Electromagnetic and Visible Spectra
Electromagnetic waves are waves that are capable of traveling through a vacuum
Mechanical waves that require a medium in order to transport their energy,
electromagnetic waves are capable of transporting energy through the vacuum of outer
space
Electromagnetic waves are produced by a vibrating electric charge and as such, they
consist of both an electric and a magnetic component
Electromagnetic waves exist with an enormous range of frequencies
This continuous range of frequencies is known as the electromagnetic spectrum
Two very narrow regions within the spectrum are the visible light region and the X-ray
region
Visible Light Spectrum
the very narrow band of wavelengths located to the right of the infrared region and to the
left of the ultraviolet region
electromagnetic waves exist in a vast range of wavelengths, our eyes are sensitive to
only a very narrow band
this narrow band of wavelengths is the means by which humans see visible light
spectrum
This narrow band of visible light is affectionately known as ROYGBIV.
Each individual wavelength within the spectrum of visible light wavelengths is
representative of a particular color
The separation of visible light into its different colors is known as dispersion
the colors red (R), orange (O), yellow (Y), green (G), blue (B), and violet (V)
visible light - the mix of ROYGBIV - is sometimes referred to as white light
Visible Light and the Eye's Response
Light that enters the eye through the pupil ultimately strikes the inside surface of the
eye known as the retina.
The cone sensitivity curve shown above helps us to better understand our response to
the light that is incident upon the retina. Since the red cone is sensitive to a range of
wavelengths, it is not only activated by wavelengths of red light, but also (to a lesser
extent) by wavelengths of orange light, yellow light and even green light. In the same
manner, the green cone is most sensitive to wavelengths of light associated with the
color green.
When a light wave with a single frequency strikes an object, a number of things could
happen. The light wave could be absorbed by the object, in which case its energy is
converted to heat. The light wave could be reflected by the object. the electrons of atoms
have a natural frequency at which they tend to vibrate. When a light wave with that same
natural frequency impinges upon an atom, then the electrons of that atom will be set into
vibrational motion. (This is merely another example of the resonance principle introduced
in Unit 11 of The Physics Classroom Tutorial.) The electrons of atoms on the material's
surface vibrate for short periods of time and then reemit the energy as a reflected light
wave. Such frequencies of lihe diagrams depict a sheet of paper being illuminated with
white light (ROYGBIV). The papers are impregnated with a chemical capable of absorbing
one or more of the colors of white light. Such chemicals that are capable of selectively
absorbing one or more frequency of white light are known as pigments get are said to
be reflected Transparent materials are materials that allow one or more of the
frequencies of visible light to be transmitted through them; whatever color(s) is/are not
transmitted by such objects, are typically absorbed by them. The appearance of a
transparent object is dependent upon what color(s) of light is/are incident upon the
object and what color(s) of lig
ht is/are
transmitted through the object.
Color perception, like sound perception, is a complex subject involving the disciplines of
psychology, physiology, biology, chemistry and physics. When you look at an object and
perceive a distinct color, you are not necessarily seeing a single frequency of light.
. Any three colors (or frequencies) of light that produce white light when combined with
the correct intensity are called primary colors of light.
The graphic at the right is extremely helpful in identifying complementary colors.
Complementary colors are always
each other on the graphic
located directly across from
Color Subtraction
Specific pigments will selectively absorb specific frequencies of light in order to produce a
desired appearance.
W - B = (R + G + B) - B = R + G = Y
C - B = (G + B) - B = G
the misconception that was targeted earlier in Lesson 2 as we discussed how visible light
interacts with matter to produce color. In that part of Lesson 2, it was emphasized that
the color of an object does not reside in the object itself
While most pigments absorb more than a single frequency (and are known as compound
pigments), it becomes convenient for our discussion to keep it simple by assuming that a
yellow pigment absorbs a single frequency. A pigment that absorbs a single frequency is
known as a pure pigment.
Pigments absorb light. Pure pigments absorb a single frequency or color of light. The
color of light absorbed by a pigment is merely the complementary color of that pigment.
Primary Colors of Paint
A trip to the local newspaper or film developing company will reveal these same
principles of color subtraction at work. The three primary colors of paint used by an
artist, color printer or film developer are cyan (C), magenta (M), and yellow (Y). Artists,
printers, and film developers do not deal directly with light; rather, they must apply
paints or dyes to a white sheet of paper. These paints and dyes must be capable of
absorbing the appropriate components of white light in order to produce the desired
affect. Most artists start with a white canvas and apply paints. These paints have to
subtract colors so that you might see the desired image. An artist can create any color by
using varying amounts of these three primary colors of paint.
Magenta paints absorb green light.
Cyan paints absorb red light.
Yellow paints absorb blue light
Blue Skies and Red Sunsets