Light and Color

Light interacting with matter

When light hits matter, at least one of three things can happen:– Reflection

When light bounces off an object

– Absorption Transfer of light energy to matter

– Makes things feel warmer

– Transmission Passing of light through matter

What type of light interactions are taking place here?

You can’t see me! Three types of materials

Translucent – matter that transmits light, but scatters it as well (you can only partially see through it)

Transparent – matter through which light is easily transmitted (you can easily see through it)

Opaque – matter that does not transmit any light (you can’t see through it)

Where do colors come from?

Remember that we see different colors of light because light waves come in different wavelengths– The longest wavelengths of visible light is seen as red– The shortest wavelengths of visible light is seen as

violet The color an object appears is determined by

which wavelengths of light are able to reach your eyes, either through reflection or transmission

Color and opaque objects

The colors of light that are reflected by an opaque object determine the color you see

White light (the combination of all colors of light) strikes this sweater. All colors of light, except blue, are absorbed by the sweater. Blue light is reflected, so it reaches your eye and you see a blue sweater

What about black and white?

White objects are white because they reflect all colors of light– The presence of all light = white

Black objects are black because they absorb all colors of light– The absence of all light = black

Mixing Light

You don’t have to mix all colors of light to get white light– You can just add red, blue and green light

together– These are the primary colors of light

Combining colors of light is called color addition

When you mix two primary colors of light, you get a secondary color (cyan, magenta or yellow)

Thanks for the compliment

Complimentary colors are two colors that create white light when shining on a surface at the same time– Ex: blue and yellow

Why are these complimentary (why do they produce white light?)

What are other examples of complimentary colors?

What is this???

A close up of a tv screen– Tv screens are

made up of little red, blue and green dots

– When electrons hit them in certain combinations, you get the various colors on the screen

Are paint and light the same thing?

Do you get white paint when you mix all of the other colors of paint?– No! so paint and light are not the same thing

Paint colors come from pigments (materials that give substances color by absorbing some colors and reflecting others)– Ex: chlorophyll (green in plants) and melanin (skin

coloring)

The primary pigments are cyan, magenta and yellow

Every pigment absorbs at least one color of light

As you mix pigments, more colors of light are absorbed so mixing them is called color subtraction

What are the secondary pigments?