Unit 7.3: Light and Color
Light is particle called a photon that travels as a transverse wave as it wiggles through space. Objects of materials that
give off or emit light are called luminous objects while those objects that only reflect light are called illuminous objects.
Materials that allow light to easily pass through them are called transparent while those materials that don’t allow light
to pass through them are called opaque. However materials that allow some light to pass through them are called
translucent. Light travels practically at the same speed all the time even though there are slight changes in speed when
it passes through materials of varying densities the number is still pretty close to the same.
The frequency at which a photon wiggles through space determines what type of electro-magnetic wave the light
represents. As shown in the graphic below, waves with the lowest frequency also have the longest wavelength and least
amount of energy. The lowest of these is a radio wave. The highest frequencies have the shortest wavelengths and the
most energy, the highest of which is a gamma ray.
The small portion of the electro-magnetic spectrum that stimulates the rods and cones in our eyes represent the visible
spectrum. Each color represents varying frequencies of light. The lowest frequency our eyes can see is red and the
highest we see is violet. In between we find variations and combinations of orange, yellow, green, and blue.
The primary colors of light are red, blue, and green. When red and blue light
are combined together we get a lighter color called magenta (a pinkish
color). When blue and green light are combined together we get a lighter
color called cyan (bright bluish like turquoise). When red and green light are
combined together we get a lighter color called yellow. If we combined all
three (red, blue, & green) together at the same time we get the color white.
The lack of light is called black.
The primary colors of pigment
are the opposite of light since
the pigment absorbs light. The
primary colors of pigment are
magenta, cyan, and yellow.
When magenta and cyan
pigments are combined together we see the color blue. When cyan and
yellow pigments are combined together we see the color green. When
magenta and yellow pigments are combined together we see the color red.
If we combined all three (magenta, cyan, & yellow) together at the same
time we get the color black. The lack of pigment is called white. All other
variations of color come from combining differing amounts of the 3 primary
pigment colors.
Polarized Light
As photons/light wiggle through space, they wiggle with various orientations. Some light is wiggling up and down,
others side to side, and others at angles. A Polaroid is a lens or a film that has little tiny slits or lines cut into it like the
gaps in a fence. When light passes through a Polaroid or polarized lens it only allows light wiggling with the same
orientation as the little slits in the lens to pass through. The rest get blocked. This causes there to be less light but still
enough to see clearly. Polarized lenses reduce the glare off smooth surfaces like windows, water, snow, and metal.
Many people used polarized sun glasses to wear when fishing, skiing, or driving to reduce the amount of light entering
their eye. If two polarized lenses are placed in sequence they can control the amount of light passing through them. If
the two lenses are oriented in the same direction as the first two fences are below, the light wiggling with the same
orientation passes easily through. However, if the two lenses are placed at 90⁰ to each other as in the second two
fences, the light that makes it through the first fence or lens does not make it through the second one. This causes no
light to pass through.
More recently 3D movies have utilized Polaroid lenses to trick the brain into believing that a 2 dimensional image is 3
dimensional on the screen. One of the lenses in the 3D glasses is vertically oriented and the other is horizontally
oriented. The movie screen has 3 pictures on it where on is vertical light, one is horizontal light, and one is at angles.
The brain takes these three pictures and puts them together in a 3D format. Before polaroids were used, 3D movies
were made by using multicolored lenses to trick the brain.