A three-dimensional gonioradiometer for the measurement of spatial power distributions is described and methods optimizing spatial resolution and duration for the determination of total power (or related photometric quantities) are reported. A silicon photodiode with known spectral responsivity is used as detector (V(lambda)-corrected for photometric measurements). The detector is moved by two frames mounted in a Cardanic gimbal suspension to give the instrument a radius of 0,3 m with a resolution of 0,01-degrees for both polar angles in more than 99 % of the full solid angle. To ensure constant total radiant power of the luminescent diodes (LED) during the sequential measurements, their electrical power is stabilized using constant electrical current and additional temperature control. Results are given for some LEDs, which are calibrated as reference standards.
