The word intensity is used in a number of similar but slightly different ways. It is sometimes defined by

where is the time-average energy flux, defined as the power P passing a given surface per unit area A.

The intensity of sound is measured using the decibel scale.

Brightness, Decibel Scale, Flux, Intensity Interferometer, Luminous Intensity, Mutual Intensity, Phase Function, Planck Intensity Density, Radiant Intensity, Radiative Transfer Equation, Specific Intensity