Why does a blue shirt look blue? DO NOW QUESTION 5/14 Why does a blue shirt look blue? Estimate 45 minutes

Unit 8: Light and Optics Chapter 21: Light and Color 21.1 Properties of Light 21.2 Vision and Color 21.3 Using Color

SWBAT explain how colors are created and observed. Objective SWBAT explain how colors are created and observed.

How Do We See Light and Color? Light reaches your eyes in one of two ways: It comes from an object that produces its own light (light bulbs, glow sticks, cell phone screen) It is reflected from objects that don’t produce their own light (clothes, plants)

Color and energy When all the colors of the rainbow are combined, we see white light. The light from the sun, light bulbs, etc. is white light. The combination of light of all colors is white light.

Prisms prove it!

Colored Light But then, why does some light look red, blue, etc.? Color is how we perceive the energy of light. Red light has low energy, violet has high energy.

Visible Spectrum Low Energy High Energy Long wavelength Low frequency High Energy High frequency Long wavelength Short wavelength

How the human eye sees light On the surface of your retina, there are special light-sensitive cells called photoreceptors. When light hits a photoreceptor, it sends a signal to your brain. The signal depends on how much energy the light has.

Some photoreceptors respond to only low energy, some respond to only high energy. That results in you seeing a certain color.

Rods There are two types of photoreceptors—rods and cones. Rods respond to differences in intensity. Rods detect black, white and shades of gray. Rods don’t need a lot of light to function.

Cones Cones respond to Color. Three types - one responds to red light, another to blue light, another to green light. When all three types are stimulated equally, we see white light.

How we see color Our eyes work according to the additive color process. Photoreceptors work together so that you see all different colors. You see different colors depending on how much energy is received by each type of cone cell.

How we see color We see different colors as a combination of the three “additive primary colors” – red, green and blue.

How we see color You can see any color by mixing percentages of red, green and blue. You see orange when you get a strong signal from red, weak signal from green.

Photons and light Light energy comes in tiny bundles called photons. Each photon carries the frequency of the light corresponding to its energy – in other words, each photon has its own color.

Energy and light Light is also a wave. Like other waves, frequency and energy are directly related – as frequency increases, energy increases.

Unit 8: Light and Optics Chapter 21: Light and Color 21.1 Properties of Light 21.2 Vision and Color 21.3 Using Color

Subtractive color process A blue shirt looks blue because it reflects blue light into your eyes. Chemicals known as pigments in the dyes and paints absorb some colors and reflect other colors.

Subtractive color process Colored fabrics and paints get color from a subtractive color process. Cyan, magenta, and yellow are the three subtractive primary colors. By using different proportions of the three pigments, a paint can appear almost any color.

The CMYK color process The subtractive color process is often called CMYK for the four pigments it uses. CMYK stands for cyan, magenta, yellow, and black.

Ink jet and color printing An ink-jet printer makes tiny dots of cyan, magenta, yellow, and black to print a full-color image. Look at an ink-jet print under a magnifying glass and the dots will be visible.

Making an RGB color image A television or computer monitor makes different colors by lighting red, green, and blue pixels in different proportions. Color images in TVs and computers are based on the RGB color model.

PHYSICS and BIOLOGY

Color Blindness 1 in 12 boys are color blind. 1 in 200 girls are color blind. It is carried on the X chromosome. Boys only need one because they are XY. Girls need two because they are XX.

Color Blindness Normal vision Green-weak color vision – lack green cones (Red and Green look the same) Red-weak color vision lack red cone, so colors with red look dark.

Plants use color Plants absorb energy from light and convert it to chemical energy in process called photosynthesis. Chlorophyll is the main pigment of plants absorbs red and blue light and reflects green light.

Why most plants are green Plants must reflect some light to avoid absorbing too much energy. The leaves of some plants turn brilliant red or gold in the fall when the chlorophyll breaks down and reveals other pigments left in the leaf.