Abstract: An optical pathway of a scanning spectral radiometer for a continuous monitoring of spectral radiation employs a diffuser having an upper source directed surface and a lower sensor directed surface for diffusing radiation incident on the upper surface and transmitting the diffused radiation. An occulting ring laterally surrounds the diffuser. A filter receives the diffused radiation from the light diffuser and passes a predetermined wavelength range. A photodetector is positioned to receive the filtered radiation. The photodetector is positioned at one end of an optical path, with a diffuser being positioned at the other end of the optical path. A collimator is provided between the diffuser and the photodetector, with the optical path extending through the collimator.