How we see color

Colors

• The color seen depends on the wavelength(s) of light an object reflects
• A red apple reflects red wavelengths and absorbs all others
• Objects reflecting all visible light wavelengths appear white
• Black objects absorb all light wavelengths and reflect almost none

Seeing Color

• The traffic light example demonstrates the importance of seeing colors for safety

Light and the Eye

• Light enters the eye through the lens, which focuses it onto the retina
• The retina, inside the eyeball, has two types of light-absorbing cells
• Chemical reactions in retina cells convert light energy into nerve signals sent to the brain

Retina Cells: Cones and Rods

• Cones are sensitive to color and bright light and there are threee types of cones in the retina
• Red cones detect mostly red and yellow light
• Green cones detect mostly yellow and green light
• Blue cones detect mostly blue and violet light
• Rods are sensitive to dim light and aid night vision

Interpreting Color

• Reflected red light from a stop sign enters your eye and focuses on the retina
• Red cone cells send a signal to your brain, which interprets it as "red"

Color Blindness

• Occurs when one or more sets of cones in your retinas do not work correctly
• Eight percent of men and one-half percent of women have a form of color blindness
• Most people with color blindness can see colors, but have difficulty distinguishing between some, usually red and green

Filtering Colors

• Filters are transparent materials that allow certain colors to pass through while absorbing others
• The color observed through a filter is the color of light that it lets through

Mixing Colors

• Pigments can be mixed to create different paint colors
• A pigment is a colored material used to change the color of other substances, and pigment color depends on the wavelengths of light it reflects

Mixing Colored Lights

• Red, green, and blue are the primary colors of light
• Mixing primary colors in different proportions produces all visible colors
• Mixing red, green, and blue light equally results in white light

Paint Pigments

• Paints are made with pigments
• Mixing red, green, and blue paint does not produce white paint
• Mixing paint is different from mixing colored light

Mixing Pigments

• Cyan, magenta, and yellow are the primary colors of pigments
• Any pigment color can be made by mixing different amounts of the three primary pigment colors
• A primary pigment's color depends on the color of light it reflects
• Pigments both absorb and reflect many colors
• Mixing equal amounts of cyan, magenta, and yellow pigments produces black
• Primary pigments are called subtractive colors because black is the result of no light being reflected