Calibration of 254-nm irradiance based on the silicon photodiode self-calibration technique.

A method of calibrating the germicidal irradiance (254 nm) based on the silicon photodiode self-calibration technique has been developed. The absolute responsivity of silicon photodiodes at 254 nm was determined by the self-calibration technique at 633 nm combined with the relative spectral responsivity measurement in the 220-780-nm region based on a standard thermal detector. By using pure 254-nm radiation, the responsivity at 254 nm was transferred to a working standard detector with a sensitivity of onlyt ~254 nm. The irradiance values measured by this detector are compared with those measured with conventional methods; for one method we used an absolutely calibrated thermal detector; for another method we used a monochromator with a spectral irradiance standard. They agreed to within a 3% difference.