Blackbody sources are uniform, temperature stable sources of infrared radiation. A blackbody is defined as either a source with zero reflectivity or a source emitting the maximum possible radiation (at all wave lengths) for its temperature. They are used for low uncertainty calibration of infrared temperature instruments. Cylindrical cavity blackbody design minimizes the effects of air movement and ambient changes.
Primary standard blackbody sources have high uniformity, so temperature instruments are calibrated by direct comparison with a contact thermometer. Secondary standard blackbody sources are first calibrated with a standard thermometer before calibrating the temperature instrument to the source. Blackbody sources can also be used with fixed-point cells where the calibration is done based on the melting point of a pure metal.