16.2 Color and Vision

Chapter 16 Objectives  Describe at least five properties of light.  Describe the meaning of the term “intensity.”  Use the speed of light to calculate the time or distance traveled by light.  Explain how we perceive color in terms of the three primary colors.  Explain the difference between the additive and subtractive color processes.  Arrange the colors of light in order of increasing energy, starting with red.  Describe light in terms of photons, energy, and color.

Chapter 16 Vocabulary Terms  additive process  black  blue  CMYK color process  color  cone cell  cyan  fluorescence  green  incandescence  infrared  intensity  inverse square law  light ray  magenta  photoluminescence  photon  photoreceptor  pixel  red  RGB color model  rod cell  speed of light  spherical pattern  subtractive process  ultraviolet  white light  yellow

Inv 16.2 Color and Vision Investigation Key Question: How do we see color?

16.2 Color and Vision  When all the colors of the rainbow are combined, we do not see any particular color.  We see light without any color.  We call this combination of all the colors of light "white light ".

16.2 Color and Vision  We can think of different colors of light like balls with different kinetic energies.  Blue light has a higher energy than green light, like the balls that make it into the top window.  Red light has the lowest energy, like the balls that can only make it to the lowest window.

How the human eye sees color  The retina in the back of the eye contains photoreceptors.  These receptors release chemical signals.  Chemical signals travel to the brain along the optic nerve.

Photoreceptors in the eye  Cones respond to three colors: red, green and blue.  Rods detect intensity of light: black, white, shades of gray.

How we see colors  Which chemical signal gets sent depends on how much energy the light has.  If the brain gets a signal from ONLY green cones, we see green.

16.2 How we see other colors  The three color receptors in the eye allow us to see millions of different colors.  The additive primary colors are red, green, and blue.  We don’t see everything white because the strength of the signal matters.  All the different shades of color we can see are made by changing the proportions of red, green, and blue.

16.2 How we see the color of things When we see an object, the light that reaches our eyes can come from two different processes:  The light can be emitted directly from the object, like a light bulb or glow stick.  The light can come from somewhere else, like the sun, and we see the objects by reflected light.

16.2 How we see the color of things  Colored fabrics and paints get color from a subtractive process.  Chemicals, known as pigments, in the dyes and paints absorb some colors and allow the color you actually see to be reflected.  Magenta, yellow, and cyan are the three subtractive primary colors.

16.2 Why are plants green?  Plants absorb energy from light and convert it to chemical energy in the form of sugar (food for the plant).  Chlorophyll is an important molecule that absorbs blue and red light.

16.2 How does a color TV work?  Televisions give off light.  To make color with a TV, you can use red, green, and blue (RGB) directly.  The screen is made of tiny red, green, and blue dots.  The dots are called pixels and each pixel gives off its own light.  TV sets can mix the three colors to get millions of different colors.