Often times, it is useful to talk about frequency instead of wavelength. The frequency is the number of times per second that wave peaks pass through a fixed location. Using both the wavelength and the speed , the frequency is calculated as:
The speed of light in a vacuum is a universal constant with value approximately equal to
m/s. In this case, in (4.1). Light propagates roughly percent faster in a vacuum than in air, causing the difference to be neglected in most engineering calculations. Visible light in air has a frequency range of roughly 400 to 800 terahertz, which is obtained by applying (4.1). As light propagates through denser media, such as water or lenses, is significantly smaller; that difference is the basis of optical systems, which are covered next.
Steven M LaValle