Approximate wavelength (in vacuum) and frequency ranges for the various colors

 

1 terahertz (THz) = 10³ GHz = 10⁶ MHz = 10¹² Hz, 

1 nm = 10^-9 um = 10^-6 mm = 10^-3 m.

The white  light is a mixture of the colors of the visible spectra.

The electromagnetic and sound specta and their use for communication

Wavelengths is a common way of describing light waves. 

Wavelength = Speed of light in vacuum / Frequency.

The speed of light is the velocity of electromagnetic wave in vacuum, which is 300,000 km/sec. Light travels slower in other media, and different wavelengths travel at different speeds in the same media. When light passes from one media to another, it changes speed, which causes a deflection of light called refraction. The index of refraction, n, is defined as the following ratio:

n = Speed of light in vacuum / Speed of light in a specific medium.