The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light. A typical human eye will respond to wavelengths from 400 to 700 nm.
White as a colour contains all the colours of the visible spectrum, it has high brightness but zero hue and is sometimes described as an achromatic colour, black is the absence of colour.
Wavelengths visible to the eye also pass through the "optical window", the region of the electromagnetic spectrum which passes largely unchanged through the Earth's atmosphere (although blue light is scattered more than red light, which is the reason the sky is blue).
Light can be split into its visible spectrum colours by using a prism, or it is sometimes seen in the sky as a rainbow. While this spectrum is made of a continuous range of colours traditionally they are commonly cited as red, orange, yellow, green, blue, indigo and violet, although recently the scientific community has changed this and now names blue as cyan and indigo as blue.
