Visible Spectrum is the band of electromagnetic wavelengths that the human eye perceives as visible light. For most people, this band extends from approximately 750 nanometers (nm), representing red light, down to 390 nm, representing violet light. The visibility curve peaks in the yellow-green region at about 560 nm; 1 nm = 0.000 000 001 meter = 10-9 m.
Also see ELECTROMAGNETIC THEORY OF LIGHT.