Light and Vision

Learning Objectives

Explain that we see objects because they reflect light into our eyes.

Distinguish between opaque, transparent, and translucent materials.

Describe how the primary colors of light (red, green, blue) combine to produce other colors.

Explain how the color of an object is determined by the colors of light it reflects and absorbs.

The Science of Sight

Light is a form of radiant energy that travels as an electromagnetic wave. Our eyes are amazing detectors that are sensitive to a small part of the EM spectrum called visible light. But how do we actually see the world around us?

How We See Objects

Most objects do not produce their own light. We see them because light from a source (like the Sun or a lamp) travels to the object and reflects off of it. This reflected light then travels into our eyes. Your eye focuses this light onto the retina at the back of your eye, which sends signals to your brain, and your brain interprets these signals as an image.

You can't see anything in a perfectly dark room because there is no light source to reflect off the objects.

How Light Interacts with Matter

When light strikes a material, one of three things can happen:

1.Transmission: The light passes through the material.

Transparent materials, like clear glass or water, allow almost all light to pass through them. You can see clearly through them.

Translucent materials, like frosted glass or wax paper, scatter the light as it passes through. You can see light through them, but you can't see a clear image.

2.Absorption: The light is absorbed by the material and converted into thermal energy (heat). A black asphalt road gets very hot in the summer because it absorbs most of the light that hits it.

3.Reflection: The light bounces off the material. A mirror reflects almost all the light that hits it.

Most objects do a combination of absorption and reflection.

The Color of Light

The white light that we see from the sun is actually a mixture of all the colors of the rainbow. We can split it into its component colors using a prism. The primary colors of light are red, green, and blue (RGB).

By mixing these three primary colors in different amounts, you can create all other colors of light.

Red + Green = Yellow

Green + Blue = Cyan

Blue + Red = Magenta

Red + Green + Blue = White Light

This is called additive color mixing, and it's how televisions and computer screens create their images.

The Color of Objects

Why is a banana yellow? Why is a strawberry red? The color of an opaque object is determined by the colors of light it reflects.

An object appears white because it reflects all colors of light.

An object appears black because it absorbs all colors of light.

A red strawberry appears red because when white light hits it, the strawberry's pigment absorbs all the other colors (orange, yellow, green, blue, violet) and reflects only the red light to our eyes.

A yellow banana absorbs the other colors and reflects yellow light (which is actually a mix of red and green light).

Key Terms

**Reflection: The bouncing of light off a surface.
**Absorption: The process by which light is taken in by a material and converted to another form of energy, usually heat.
**Transmission: The passing of light through a material.
**Transparent: A material that allows light to pass through it without scattering, so that objects on the other side can be seen clearly.
**Translucent: A material that scatters light as it passes through, so that objects on the other side are blurry.
**Opaque: A material that reflects or absorbs all of the light that strikes it, so that you cannot see through it.
**Primary Colors of Light: Red, green, and blue (RGB). When mixed, they produce white light.