A radiometer composed of a silicon photodiode, interference filter, and integrating sphere was characterized and calibrated against an absolute silicon detector standard at 600 nm using a CW dye laser. This radiometer was then used to measure the irradiance at 600 nm from spectral irradiance lamps calibrated against a gold point blackbody, and also the irradiance from the NBS electron storage ring, SURF II. These results were intercompared with the independently calculated irradiances from these two sources, with overall agreement of better than one percent. Various aspects of the measurements are discussed.
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