Book excerpt: This book discusses modern, user-friendly radiometric practices that make it possible to convert from traditional source-based optical radiation measurements to the more efficient and higher accuracy detector-based applications and calibrations. It considers improved performance optical detector and radiometer standards including photometers and tristimulus colorimeters, and describes research-based design considerations, measurement of radiometric, optical, and electronic characteristics, and comparison of absolute-, transfer-, and working-standard detectors and radiometers from the ultraviolet (UV) to the infrared (IR) range. The book will serve to guide the optical radiation measurement community, researchers, manufacturers, calibration laboratories, students, and practicing engineers to switch from the old and limited-use measurement methods to the higher performance detector-based applications. The radiometer standards discussed here can be used to produce wide range radiometric, photometric, colour, and radiation temperature measurements with low uncertainty.