The universe is everywhere surrounded by electromagnetic waves of different lengths. Light is the portion of the spectrum that stimulates the retina of the human eye allowing the perception of colors.
This region of the electromagnetic waves is called Visible Spectrum and occupies a very narrow band of the spectrum.When light is separated into its various component wavelengths is called spectrum.
If the light is passed through a prism of transparent glass, it produces a spectrum consisting of red, orange, yellow, green, blue, indigo and violet. This pnenomenon is caused by differences in their wavelengths. Red is the wavelength of the longest and the shortest violet. The eye humano percibe these different wavelengths and colors.
The spectrum visible to the human eye is one that goes from the 380nm wavelength for violet to 780 nm for red color. Outside these limits, the eye does not perceive any kind of radiation.