Optical radiation is an electromagnetic wave. The waves at different lengths contribute to the radiation spectrum and the separated wavelengths form a range. In other words, the wavelength is a distance between two recurring wave elements - Fig. 1.
Optical radiation can be classified as:
The following optical wavelengths correspond to each range:
780 - 1 000 000 nm
380 - 780 nm
10 - 380 nm
Fig. 2. Visible radiation spectrum with optical wavelength corresponding to a specific colour