1. Lecture 49 Light and Color Ozgur Unal
NIS – PHYSICAL SCIENCE
Lecture 49
Light and Color
Ozgur Unal

2. Why Objects Have Color?
How many colors are there in the Philippine flag?
Why do some objects appear red, while others look green or yellow?
How about white and black?
When a red apple is struck by white light, it reflects red light back to your eyes and absorbs all of the other colors.
White objects reflect all colors.
Black objects do not reflect any color, they absorb all colors.

3. Colored Filters
A filter is a transparent material that transmits one or more colors of light but absorbs all others.
The color of a filter is the color of the light it transmits.
Check out Figure 25.

4. Seeing Color Light and the eye: In a healthy eye, light enters the
eye through the cornea.
Retina is made up of two types
of cells that absorb light: cone cells
and rod cells.
Cone cells need bright light to
generate nerve impulses.
Cones do not operate in dim
light  even brightly colored objects
might look gray or black in dim light.
3 types of cones: red cones, green
cones and blue cones

5. Seeing Color Rod cells are sensitive to dim light and enables you
to see at night.
Rod cells are mostly located
around cone cells.
Humans have many more rod cells than cone cells  this enables us to see at night.
How about nocturnal animals?
Infer the number of rods in the
eyes of these animals.

6. Color Blindness Can you read the number below?
The most common form of color blindness makes it difficult to distinguish between red and green.
8% of men and 1.5% women are color blind.

7. Mixing Colors The colors are a result of mixtures of pigments.
Blue + Yellow  Green
A pigment is a colored material that is used to change the color of other substances.
The color of a pigment results from the different wavelengths of light that the pigment reflects.
Mixing Colored Lights:
All colors can be made by mixing
three colors of light: blue, red and
green  primary colors
Mixing primary colors in equal
amounts gives white.

8. Mixing Colors Paint Pigments:
If you mix equal amounts of red, blue and green paint do you get white?
Paints are made with pigments.
Pigments produce color as a result of the wavelengths of light they reflect.
Mixing Pigments:
You can make any pigment color
by mixing three primary pigments:
magenta (bluish red), cyan
(greenish blue) and yellow.