The effect of irradiation by several spectral bands in the visible region on the charge transferred by the pulses occurring in the Siemens' type ozonizer discharge through hydrogen due to d.c. excitation has been studied. It has been observed that the charge transferred per minute is reduced under irradiation. This reduction is found to be independent of the potential applied to the discharge tube in the range 800-1200 v. On the other hand, the reduction in the charge transferred increases with the intensity and the frequency of radiation. The plots between the charge transferred and the logarithm of intensity are linear; the slope of these lines reduces with the increase in the wavelength of radiation. These plots suggest that there may be a long-wavelength limit beyond which the Joshi effect would not be observed. Any such limiting wavelength exceeds 600 nm under the present experimental conditions. The results can be explained on the basis of photoelectric emission from the adsorption-like boundary layers on the ozonizer, as postulated by Joshi.

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