CIE 237:2020 gives recommendations for the characterization, selection and application of optical radiation detectors to perform linear measurement conditions. It helps the users to find the causes of non-linear behaviour and to avoid non-linear operation. It discusses detector operating circuits, measurement conditions, detector signal measurements in different modes, and preamplifier measurements. It is shown how to produce a detector system that minimizes measurement uncertainties caused by non-linear operation. Non-linearity test methods and procedures are discussed by which the linearity of detectors and their operating circuits can be determined.[more]