The wavelength of a wave is the distance between two repeated points, as shown in the figure above. The period T of a wave is the time it takes for an entire cycle of the wave to pass one point in space. In the animation below, one complete cycle passes the green line in 5.0s, so the period of the wave is 5.0 s. (The timer may or may not represent real time, depending on your system.) Click on "replay" to see the animation again.
The wave speed is the speed at which one point in the cycle travels through space. Since any point on the wave will travel one wavelength of distance in one period of time, the speed v can be found from
Light can be represented by sine waves, wave fronts, or arrows in the direction of motion, as the animation below illustrates. Click on "replay" to see a given animation again. When you have viewed animation 1, click on the "2" in the bottom right to continue, then "3", then "4".
A particular representation (waves, wavefronts, and rays) may be better
suited for a given context, but all three representations are equally valid
ways of illustrating light.