Sun is the main light source of the earth. Nearly half of the electromagnetic radiation range reached from the sun to the earth is the visible light. Visible light can be sensed by the human eye and is essential for the visual sense. It has a wavelength range between 400-700 nm, between infrared and ultraviolet light. We see light beems in different colours according to their changing wavelengths. The main colours are red, blue and green. The combination of them is seen as white, the abscence of them is seen as black.
The physical property of light plays a role for the human eye, as the diffraction of the light on the pupil margin or the aberation of the light in peripheral cornea or the different refractive features of the light according to its colour. These properties are important in refractive surgery (excimer laser treatment).