Detector calibration methods are described which enable the measurement of absolute power. The method includes using a power meter with traceability to the national standard for optical power to calibrate the power of each photodetector device of a detector with photodetector device arrays arranged in one dimension or two dimensions and to calibrate the output signals of the detector making it possible to measure the spatial distribution of a light source's power and also values of optical power with traceability to the national standard directly from the output signals of the detector.