The Remote Sensing Group at the University of Arizona has developed multispectral ground-viewing radiometers that use light-emitting diodes as detectors. This work describes the optical design, electrical design, and laboratory calibration of a three-channel radiometer that operates in the visible and near-infrared region of the spectrum. The optical and electrical design of the radiometer is introduced, and then the calibration and characterization of the radiometer are described. Laboratory measurements include the spectral responsivity for each channel of the radiometer, the temperature dependence of the total responsivity for each channel, system linearity, field of view, and finally, the absolute radiometric calibration. A solar-radiation-based calibration is used to determine the absolute responsivity.