The electromagnetic spectrum gives the range of all the different kinds of electromagnetic radiation. Visible light is part of the electromagnetic spectrum, but it covers only a small portion of the spectrum.
The spectrum categorizes the different radiation types according to the length of the waves. Radiation with wavelengths longer than visible light include infrared rays and radio waves. Radiation with wavelengths shorter than visible light comprises ultraviolet light and gamma rays. The only part of the electromagnetic spectrum detectable by humans is visible light; all other radiation is considered invisible.
Radiation can also be measured using the frequency of the waves. Waves with longer wavelengths have lower frequencies whereas those with shorter wavelengths have higher frequencies.