FREE ESSAY ON THE VISIBLE LIGHT SPECTRUM

THE VISIBLE LIGHT SPECTRUM

"Mr. Petersuh-uh-uhn…. I need a white crayon for the white parts of the map!", my
daughter's classmate whines as she peers into her box of mismatched Crayons. "Don't worry
about coloring those parts of the map. White isn't a color anyways…", replies her
sixth grade teacher. Uh-oh. Big mistake! The entire class is now in for an impromptu
lesson in the properties of light and the visible spectrum, courtesy of the child of a
laser student. Added bonus: elevated egg-headed status for aforementioned child.
"Excuse me, Mr. Petersen, but I feel that I must correct you on that. You are sadly
misinformed. My Mom says that white is the presence of all color and black is no color!
What of that?! Hmmm?" (Yes…my kid really talks like this. She's 10 and she skipped
a grade level. She's quite loquacious. I wonder where she gets it from? But I
digress…)
The flustered Mr. Petersen flashes my child a weak smile and mumbles something to the
effect of, "…technically, Jacki, you are correct. Just leave the white parts blank
and stay on task!" Shame, shame, shame. The instructor has just dropped the ball on a
wide-open opportunity for learning and discussion. 
Never one to miss an opportunity to exercise her mind and initiate a discussion/impress
her peers, my kid goes on to explain the basic principles and properties of light and
color. This precipitates a wave of "no way!" and "how'd you know?"s from the inherently
curious and doubly impressed group of sixth graders.
As she, in fits and giggles (true sixth grade girl fashion!), recounted the story to me,
she re-iterated over and over that "most grown ups just don't know ANYTHING!". And I
thought to myself, "You know…we might know a lot about some things, but she just
pointed out one of the most popular misconceptions that abounds concerning light and the
perception of color!". White light is NOT the absence of all color! Black is NOT all of
the colors all mixed together! (Remember second grade? When you ran out of black crayon
and just scribbled all of the remaining colors together and got a muddy brownish gray at
best? Uh-uh…never works.)
Thus, I have taken it upon myself to enlighten the rest of us "just don't know ANYTHING"
grown-ups on the subject of color and the visible spectrum of light. Pay attention,
class! This is Visible Light 101.
All light consists of waves traveling in space. The length of the waves determines the
color of the light. Each color of light has its' own characteristic wavelength and what
is visible to the human eye is termed the visible spectrum of light. It begins on one end
with the color red and goes through the spectrum to the color violet. The entire spectrum
consists of the following colors: red, orange, yellow, green, blue, indigo, and violet.
White light consists of a mixture of many different wavelengths. Try this: use a prism to
disperse white light from a source such as a light bulb or flashlight into its' separate
component (colors).
The fact that we "see" a certain color at all is dependent on a couple of basic
principles. First, ordinary colored light consists of a broad range of wavelengths
covering a particular portion of the spectrum. When you isolate those wavelengths, by
using a filter or a device that blocks the undesired wavelengths, you will see only the
ones that are emitted when you view the light. A good example of this is a stop
light… the green light emits the entire green portion of the spectrum plus a little
of the neighboring yellow and blue regions.
Other reasons for seeing only certain colors are attributed to the four properties of
light know by the acronym RATS. R.A.T.S stands for reflection, absorption, transmission,
and scattering. Each of these processes occurs to some degree when light is incident upon
a surface. In the case of the color white, most or all of the wavelengths are reflected
back to your retina, allowing you to see the entire visible light spectrum. In the case
of the color black, most or all of the available light that is incident upon the surface
being viewed is absorbed by the surface. This leaves little or no part of the visible
spectrum to be reflected back to your eye. So you see none, or very little of the visible
spectrum. Impress your kid. Class dismissed.