Abstract: The principle and technology behind the measurement of the emission parameters of light emitting diodes(LEDs) are described with regard to their spatial and spectral power distribution. The basic concepts, measurment methods and mutual relationship of radiant flux and luminous flux are discussed. In practice, the radiant power and luminous intensity are the most important parameters. The spectral power distribution and main colorimetric parameters are discussed according to the colorimetry based on human vision, with mention also of calibration standards.