Light, Polarization & Color

The nature of an object’s color

• What are examples of color?

• How can we tell one shade of a color from another?

• Do objects seem to sometimes change color under different light conditions?

White Light

Def: light given off from a source that emits all colors of light at once.

Light from a light bulb isn’t just one color, it’s three!

Primary Colors

• There are only three primary colors:

• Red, Green, and Blue

• ALL other colors can be made by mixing these together.

Complimentary Colors

• Mixing two primary color together makes one of the complimentary colors:

• Red + Green = Yellow

• Green + Blue = Cyan

• Blue + Red = Magenta

The Color White

• If you mix all three primary colors together, they will appear to be the color white.

• There are an infinite number of color combinations of Red, Green, and Blue to create different “recipes” of color.

Overlapping Colors Of Light

Creating the rainbow…

• Smoothing out the colors would make the diagram look something like this.

What’s different about colors?• Each color of light has it’s own specific

wavelength.

So….

• If every color has a different wavelength, maybe they behave differently when different colors of light hit the same object.

• This is what gives an object it’s color.• (At least, what we think it’s color is)

Everything’s a Mirror

• Almost all objects reflect some kinds of light and absorb other kinds.

• White objects reflect all colors of light.

• Black objects absorb all colors of light.

• Absorbing light transfers energy to an object, so black objects heat up more rapidly than white objects.

Everything’s a Mirror

• Objects in between only reflect certain kinds of light.

• Example: Green leaves reflect green light, but absorb all other colors of the rainbow.

When’s a White shirt not white?

• A white tee shirt reflects all colors of light, making it appear white.

• If you look at a white shirt under red light, it looks red, because it’s reflecting all the light that’s there (only red), so that’s what you see.

Light Waves

• Since light travels in waves, they would look like this from the side:

• But this from the front

Light in the real world

• Looking at a beam of light from the front, individual waves might look like this:

Polarizing Lens

• A polarizing lens only allows light waves lined up in a certain direction to pass through.

• A lens looks like the boards on a deck:

Polarizing Lens

• Only light that will “fit between the cracks” will pass through the lens. All the other light waves bounce off.

• Only these three ray will pass through

Uses of Polarized Light

• Polarizing Lenses can be used in the lab in experiments, but practical applications are:

• Sunglasses• Window Tint• Video Cameras• Binoculars/ Telescopes

• Using Polarizing lenses helps reduce glare and increase visibility in optics applications.

Practice

• To practice with these concepts, complete the Section Review on Pg. 474 #1-4.