An on-line ultraviolet radiation monitoring system for control of photosensitivity test dose.

A system has been developed to monitor and integrate on-line a small fraction of the monochromatic ultraviolet radiation directed at the skin from a phototest source, thus correcting for fluctuations in the irradiance. On completion of the required test dose, the exposure is terminated automatically. Radiation is reflected from a silica plate, housed in a skin applicator, onto a photodiode connected to an integrator. The variation of the reflectivity of the silica plate with wavelength and with incident angle was calculated. The reflectivity of the applicator with and without the silica plate in situ was studied experimentally. Measurements were made of the spatial distribution of irradiance from and across the face of the applicator. To calibrate the photodiode current, the absolute irradiance at the face of the applicator had to be measured with a wide angle detector. No significant deviation from a linear variation was observed between changes in the skin irradiance and changes in the photodiode current.