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.
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.
time you see a nice bright, clear rainbow, best of all against a dark
yourself: Are each of the 150 colors, lined
up across a section of rainbow, EQUALLY BRIGHT?
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
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
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
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
Out of the
150 colored lights we humans can distinguish, vision is most
sensitive to exactly three particular colors:
These are the
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
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
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.
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.
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.
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
A dark barren planet...off
Then, there may be light,
but there is no COLOR...
until there is a
being to SEE color.
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!)
going deeper into COLOR,
let’s consider LIGHTS more carefully.
IS NATURAL WHITE LIGHT?
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,
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
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.
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
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.
“particular kind of ray” cannot be changed in color.
“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
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.