Electromagnetic radiation that is visible to the human eye; also referred to as radiation enabling visual perception. We see light in the form of colour. The wavelength range is 0.38 to 0.76 μm.
Blue light is EM radiation with a wavelength of around 0.45 μm. Red light, at the other end of
wavelength the colour spectrum of a rainbow, has a wavelength of around 0.65 μm (Figure 1). Electromagnetic radiation outside the range 0.38–0.76 μm is not visible to the human
eye.