An intercomparison has been conducted among three independent scales of spectral irradiance: two source-based and one detector-based. Specifically, a radiometer composed of a silicon photodiode, an interference filter, and an 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 spectral irradiance at 600 nm from spectral irradiance lamps calibrated against a gold-point blackbody, and the spectral irradiance at the same wavelength from the NBS electron storage ring, SURF-II. Intercomparisons of this type are an important check of the agreement between these independent radiometric techniques. It was found that the detector scale indicated a spectral irradiance at 600 nm that was 0.76% lower than predicted by the gold-point blackbody scale and 0.25% higher than predicted by the electron storage ring scale. This result implies agreement within the overall quadrature uncertainties of ±0.25% for the detector scale, ±0.84% for the gold-point blackbody scale, and ±0.60% for the electron storage ring scale.