The Tri Color Story, Prime Color Incorporated, Inc.

Let's start at the beginning....

The rainbow, formed from droplets of water in sunlight, contains all 150 of the brilliant colors that the vision of man can distinguish. Each water droplet acts as a prism.
Other light sources that might form a visible rainbow (a street lamp, an oncoming car headlight---) may or may not contain all 150 colors.
Some streetlights contain only a few colors in their lights, so they may cause funny-looking rainbows.
Light from the sun, moon, and planets all contain all the visible colors, since they shine by direct or reflected sunlight.
Mars does, too, but it reflects more red, than blue, for example, so reddish colors in its rainbow will be relatively stronger than its bluish colors.

But, so far as human vision is concerned, some of the rainbow colored lights are much more important than some others.

The power in sunlight is remarkably evenly spread across the visible spectrum, which means that in a normal rainbow, the power content of each of the 150 colors is about the same.

Next time you see a nice bright, clear rainbow, best of all against a dark cloud, ask yourself: Are each of the 150 colors, lined up across a section of rainbow, EQUALLY BRIGHT?

Now here's a surprise.

Observe carefully, for 2300 years ago a fellow named Aristotle noticed in the rainbow that blue, green and red are very much brighter than, for example, violet, blue-green, yellow, and deep red. This is still noticeable today.

BUT, the rainbow DOES have about the same power content in each of the 150 colors. So, what makes the difference?

The difference is in US..human vision. Human beings cannot see the last four colored lights as well as we can see the first three. More accurately, perhaps, we respond much more weakly to a little yellow light coming into our eye than we do to a little green light, when both have the same power content.

You know about watts of power, and the brightness of incandescent bulbs. A hundred-watt bulb in your living room lamp emits about 25 watts of yellowish light (and the other 75 watts as heat) and the 25 watts can illuminate the whole room. Perhaps five or ten watts of green light would look as bright.
These days we understand that, deep in the human visual system, probably near the back of the head, there are three separate components of vision, sorting out what is seen into three separate channels--- one sensitive to bluish lights, one to greenish, and one to reddish parts of the light coming into the eye.
Out of the 150 colored lights we humans can distinguish, vision is most sensitive to exactly three particular colors:

Blue-violet Pure green Orange-red

These are the “prime colors.” (or PCs)

The other 147 colors just don't stimulate the vision as much. In a real sense, the normal human visual system WATCHES FOR the three prime colors.
Rainbows are not the only place we see the prime colors!! The rainbow is only a dispersing agent, showing that the PCs are present in all natural white lights. (and even all natural lights of all colors, since the colors at sunrise and sunset, no matter how vivid, include the same 150 colors, and so include the Prime Colors.
The unique thing about the rainbow is NOT that it contains the PCs (because so many other lights do also) but that it DISPERSES the sunlight so we can see which of the 150 colors are present.
In general, no matter what objects reflect natural phases of daylight, they always seem to reflect at least a little of ALL of the 150 colors. Even a ripe tomato, although its reflectance in the red is 70-80%, reflects at least one percent or a few percent of the other visible wavelengths.

As the years go by, the white light of illumination will gradually evolve to be a pure mixture of the three prime colors. Also, the light from movie screens, from football-game score boards, televisions, traffic lights, electric signs, and every sort of light or image destined to be seen, will be composed of the three prime colors. This is the future of lighting.

First reason: This is the least expensive way to go. Using lights that draw the human visual attention will be the most efficient, lowest use of power content.
Second reason: It allows greater clarity of seeing. Oddly, at least at first glance, the more of the colors: violet, blue-green, yellow, and deep red find their way into the eyes, the less clear the image becomes.
Third reason: It brings about pleasant coloration. Illumination composed only of a mixture of the prime colors shifts the colors of all of the illuminated objects in directions deemed to be most pleasant to the beholder. This was discovered and tested using identifiable test objects: objects most important to the usual observer, such as complexions, fruits, vegetables, meat, bread, grass --- objects whose colors are EXPECTED by the human viewer.

NOW HERE'S THE FULL STORY>>>>>

A dark barren planet...off in space...
first needs LIGHT...

Then, there may be light,
but there is no COLOR...

until there is a living being to SEE color.

If the living being is a PRIMATE, then it sees color just as we humans do.

(we humans are called “primates.” “primates” means “first” --- so of course we saved the “first” category for ourselves!)

Before going deeper into COLOR, let’s consider LIGHTS more carefully.

WHAT IS NATURAL WHITE LIGHT?

SUNLIGHT is most natural to us

Sunlight is a mixture of colored lights, each of a different wavelength.

We are indebted to the rainbow for revealing these colored lights,
in all their glory.
The pictured rainbow records one of those rare instances in which the rainbow is backed by a dark cloud, making the brilliance of the colors more apparent.

The shortest wavelength we can see comfortably is VIOLET in hue. From violet, the hue runs: violet, blue- violet, blue, blue-green, green, yellow- green, yellow, yellow-orange, orange, orange-red, red. But happily there are about 150 distinguishable colors as is seen more clearly in the next picture. Thank heaven we don’t have to memorize their names!

Think of 150 very narrow vertical slices here. The wavelength of pure violet light is near 400 nanometers. (There are about 25,000,000 nanometers in one inch, which is no help, is it?)
But the beautiful spectrum laid out above gives some idea of the brilliant color embodied in these lights which, mixed, make our daylight.

You all know that it is drops of rainwater, acting like small prisms, that separate and disperse these colors.

Here is the remarkable scientist in whose laboratory white light was first dispersed into these many colors: Isaac Newton

He reported it to the Royal Society of London in 1671 (if you can believe it).

He captured a ray of sunlight coming in through a small hole in his black shade, dispersed the white light with a glass prism, then tried to split the rainbow further, and found he could not. Any “particular kind of ray” cannot be changed in color.

Isaac Newton “disclosed the origin of color,” as he put it, to be a matter of wavelength of the light. For us, the next step is to begin to understand, on this basis, exactly how any light is physically described.

We know that any light (except the pure colors of a single wavelength) is a mixture of colored lights. In the next figure, we see how much power ( in watts) resides in a light.