Light Visible Light Visible Light the range of

Light

Visible Light • Visible Light - the range of frequencies of electromagnetic waves that stimulates the retina of the eye

Visible Light • The lowest frequency of light we can see is red light • The highest frequency of light we can see is violet light • EM waves with frequencies lower than red light are called infrared • EM waves with frequencies higher than violet light are called ultraviolet

Sources of Light • Luminous source: emits light waves (Sun, light bulb) • Illuminated source: reflects light waves (Moon)

What happens to the light? • When light waves strike an object, the waves can be: – Absorbed by the object – Reflected by the object – Transmitted by the object

Light and Matter

Transparent • Materials that transmit light waves • Examples: –air –glass –some plastics

Translucent • Transmit light but do not permit objects to be seen clearly • Examples: –lamp shades –frosted glass

Opaque • Transmit no light • Absorb or reflect all light waves

• http: //www. ted. com/talks/beau_lotto_optica l_illusions_show_we_see. html

Color Newton determined that white light was made from a combination of color

Additive Color Mixing • White light = RED LIGHT + GREEN LIGHT + BLUE LIGHT • These are considered Primary Light Colors

Adding colors • White light can be split up to make separate colors. These colors can be added together again. Adding blue and red makes magenta (purple) Adding red and green makes yellow Adding blue and green makes cyan (light blue) Adding all three makes white again

Secondary Light Colors • Formed by mixing primary colors –Yellow –Magenta –Cyan

Complementary Colors • Two colors that add to produce white light – Cyan and Red – Magenta and green – Yellow and blue

For more practice with mixing colors of light: http: //www. physicsclassroom. com/Physics. Interactives/Light-and-Color/RGB-Color. Addition/RGB-Color-Addition-Interactive

Seeing color • The color an object appears depends on the colors of light it reflects. For example, a red book only reflects red light: White light Only red light is reflected

A pair of purple pants would reflect purple light (and red and blue, as purple is made up of red and blue): Purple light A white hat would reflect all seven colors: White light

Filters • A filter can be used to block certain colors of light • Filters allow only certain frequencies to be transmitted. • For additional help with filters go to: – http: //www. physicsclassroom. com/Physics. Interactives/Light-and-Color/Color-Filters

Using filters • Filters can be used to “block” out different colors of light: Red Filter Magenta Filter

• http: //www. michaelbach. de/ot/col_mix/inde x. html • A cyan filter absorbs red light, the magenta filter absorbs green light, and the yellow filter absorbs blue light.

Making Color by Subtraction • Objects can reflect and transmit light, and they can also filter light. • Colored filters transmit certain frequencies of visible light while absorbing others. • A blue filter absorbs red and green, a red filter absorbs green and blue, and the green filter absorbs red and blue.

Primary Pigment • Pigments are like dyes except they are made of minerals. • Primary pigments absorb only one primary color of light. This means they reflect 2 colors of light. • The primary colors of pigments are yellow, cyan and magenta. • A color printer uses the primary colors of paint to produce any color imaginable.

Secondary Pigments • A pigment that absorbs two colors of light and reflects one is a secondary pigment. • The secondary pigments are red, blue, and green. • The primary pigment colors are the secondary light colors and the secondary pigment colors are the primary light colors.

Complementary Pigments • Red pigment is complementary to cyan. • Blue pigment is complementary to yellow. • Green pigment is complementary to magenta. • Complementary pigments are those that when mixed, result in a black color.

Color Blindness • http: //colorvisiontesting. com/ishihara. htm

Using colored light • If we look at a colored object in colored light we see something different. For example, consider the following: Shirt looks red White light Shorts look blue

• In different colors of light these clothes would look different: Shirt looks red Red light Shorts look black Shirt looks black Blue light Shorts look blue