Download Chapter 28 Color

Chapter 28
Color
Spectrum:
The spread of colors seen when
light is passed through a prism or
diffraction gradient.
That is, when light of that
particular wavelength strikes the
retina of our eye, we perceive
that specific color sensation.
Each individual wavelength
within the spectrum of visible
light wavelengths is
representative of a particular
color.
When all the wavelengths of the
visible light spectrum strike your
eye at the same time, white is
perceived.
White light:
Light that is a combination of all
colors. Like sun light.
White is not a color but a
combination of all colors.
Black is also not a color but the
absence of the wavelengths of
the visible light spectrum.
So when you are in a room with
no lights and everything around
you appears black, it means
that there are no wavelengths of
visible light striking your eye as
you sight at the surroundings.
The way we see color is by the
reflection of color off of a
surface. The colors that we see
are reflected off a surface while
the other colors are absorbed
by the surface.
You look at a flower and see a
green stem. The stem absorbs
all other colors and reflects
green.
Pigment:
material that selectively absorbs
colored light.
A red piece of class appears red
because it absorbs all the colors
that compose white light, except
red, which it transmits.
If an object absorbs all of the
frequencies of visible light
except for the frequency
associated with green light, then
the object will appear green
Additive Primary Colors:
Any three colors (or
frequencies) of light which
produce white light
Red, Green and Blue are the
three primary colors of white
light.
Color television is based on the
ability of the human eye to see
combinations of the three colors
as a variety of different colors.
Pixels in the screen are set to be
red, green or blue. Depending on
how you adjust their brightness
you will get different colors.
Complementary Colors:
When 2 colors are added
together to produce white.
Red and cyan = white
green and magenta = white
yellow and blue = white
Mixing colored paints is different
than mixing light. If you mix red
and green paint you get brown.
Paints do not reflect a single
color of light. They reflect
several colors.
Color subtraction is on page
429 – 431.
Read these pages.
Why is the Sky Blue?
The atmosphere is a gaseous
sea which contains a variety of
types of particles. The two most
common are gaseous oxygen
and nitrogen.
These particles are very
effective in scattering the higher
frequency, lower wavelength
portions of white light. Which
means that Blue, Indigo, and
violet are scattered.
The lower frequency, longer
wavelength waves are more
likely to get through.
This scattering of the higher
frequencies of light illuminates
the skies with light on the BIV
end of the visible spectrum.
Compared to blue light, violet
light is most easily scattered by
atmospheric particles; however,
our eyes are more sensitive to
light with blue frequencies.
Thus, we view the skies as
being blue in color.
As you leave our atmosphere
the particles in the air get fewer
and fewer so less of the light is
scattered so it will appear black.
Like on the moon.
Why are sunsets Red?
Because when the sun is low in
the sky it has more of our
atmosphere to travel through
allowing the lower frequency
colors to be scattered also.
During sunset hours, the light
passing through our
atmosphere to our eyes tends to
be most concentrated with red
and orange frequencies of light.
For this reason, the sunsets
have a reddish-orange hue
Why is water greenish – blue?
Read pages 435 - 436