In a wave diagram, amplitude is represented as the distance from the centre line (or midpoint) of a wave to the top of a crest or the bottom of a corresponding trough.
When the amplitude of an electromagnetic wave increases, the overall distance between any peak and the next trough also increases.
The quantity of energy carried by an electromagnetic wave is proportional to the amplitude squared.
Amplitude has an indirect correlation with the perception of the intensity of light and the brightness of colour as perceived by an observer because additional factors such as phase and interference must be taken into account.