Photons - Electromagnetic spectrum

EM Spectrum - visible light
(ref)

Electromagnetic radiation (EMR) is a form of energy emitted and absorbed by charged particles, which exhibits wave-like behaviour as it travels through space. (In vacuum, electromagnetic radiation propagates at a characteristic speed, the speed of light.)

EMR is classified according to the frequency of its wave. The electromagnetic spectrum (EMS), in order of increasing frequency and decreasing wavelength, consists of

• radio waves 
• microwaves 
• infrared radiation 
• visible light 
• ultraviolet radiation 
• X-rays 
• gamma rays 

EMR covers wavelengths from thousands of kilometres down to a fraction of the size of an atom.

The limit for long wavelength is the size of the universe itself,

The short wavelength limit is in the vicinity of the Planck length, although in principle the spectrum is infinite and continuous.

The electromagnetic spectrum is highly studied for spectroscopic purposes to characterize matter.


The eyes of various organisms sense a small and somewhat variable window of frequencies of EMR called the visible spectrum.

(Based on wikipedia article on EMR)