Spectral sensitivity
 
Any detector is not equally sensitive to energy of all wavelengths. By this we mean that if a series of recordings is made whereby the detector is illuminated by radiation from different spectral wavebands but each containing equal amounts of energy, its recorded response varies according to the position of the waveband in the spectrum. The way in which the detector responds to equal amounts of energy at different wavelengths is described by its spectral sensitivity curve, S(λ). This curve of spectral response is frequently depicted in a relative way by setting the maximum value of S(λ) equal to unity.