Ray model of light Travels in a straight line Only see light when it goes into your eye Changes direction at boundaries

Sources of Light Luminous Sources – emit light (sun, lamp) Illuminated sources – reflect light (moon, objects)

Light and Matter Opaque – object that does not transmit light (notebook) Transparent – object that transmits almost all light (glass) Translucent – object that transmits some light and reflects some light (frost glass)

Polarization Polarized light—light waves that vibrate in a single plane Polaroid filters block one plane of light waves

Color and Vision When all the colors of the rainbow are combined, we see "white light".

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 Photoreceptors in the retina (back of eye) send chemical signals to the brain 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 ENERGY determines the chemical signal that is sent If the brain gets a signal from ONLY green cones, we see green.

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. 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 The light that reaches our eyes from an object can be: Emitted directly from the object (light bulb or glow stick) Reflected by the sun or other light source

Color By Subtraction Colored dyes get color from a subtractive process. Chemicals, known as pigments, in the dyes absorb some colors Colors that are not absorbed are reflected, and you see them Magenta, yellow, and cyan are the three subtractive primary colors.

Green light on a magenta surface appears colorless because green is absorbed Magenta light on a green surface appears colorless because magenta is absorbed Magenta in Green in No color No color Magenta surface absorbs (subtracts) green. Green surface absorbs (subtracts) red and blue (magenta).

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.

Application: Color Printing