We know that all electromagnetic waves propagate in a vacuum with the speed of light. Electromagnetic waves transport momentum and energy away from a source. It is important to remember that electromagnetic waves differ by their frequency and wavelength, and the interaction of these waves with matter depends on the frequency of the wave and the atomic-molecular structure of matter.
The simple form of electromagnetic waves corresponds to the electromagnetic spectrum that our eye can see. Light is produced by bodies that are at high temperature (like the filament of a light bulb) and by the reorganization of electrons into atoms and molecules.
The wavelengths of visible light are classified according to the color, from violet, which has wavelength λ = 4 . 10 -7 m, to red, whose wavelength is λ = 7 . 10 -7 m. Therefore, eye sensitivity is a function of wavelength and is maximum for a wavelength λ = 5.5 . 10 -7 m (yellow-green). Vision is the result of signals transmitted to the brain by two elements present in the retina: cones and rods.
Cones are elements that activate when there is intense light (such as during the day); and are color sensitive. The rods, on the other hand, are elements capable of working with less intense lighting (as, for example, in a darkened room); and are less sensitive to color.
Light is so important that it gave rise to the development of a special branch of applied physics: optics. This science studies the phenomena related to light and vision, also including the design of optical instruments.
