The range of linear operation of Si photodiodes is defined relating the two limits of the range to the required precision of the measurement. The two limits are given by the noise equivalent power (NEP) and the maximum permissible deviation in the transition region from linear operation to saturation. Data on the linearity ranges of commercially available photodiodes are given.
W. Budde, "Definition of the linearity range of Si photodiodes," Appl. Opt. 22, 1780-1784 (1983)