Imagine you are indoors on a sunny day. A beam of sunlight through a window lights up a section of the floor. How would you draw this sunbeam? You might draw a series of parallel lines showing the path of the sunlight from the window to the floor. This is not exactly accurate — no matter how hard you look, you will not find unique lines of light in the sunbeam! However, this is a good way to draw light and to model light geometrically.
We call these narrow, imaginary lines of light light rays. Recall that light can behave like a wave and so you can think of a light ray as the path of a point on the crest of a wave.
We can use light rays to model the behaviour of light relative to mirrors, lenses, telescopes, microscopes, and prisms. The study of how light interacts with materials is called optics.
When dealing with light rays, we are usually interested in the shape of a material and the angles at which light rays hit it.

License information: CC BY 3.0
MPAA: G
Go to source: https://drive.google.com/file/d/0Bz69EszGvRvaYnlFU1Zfb0hHNXc/view