Abstract: The invention relates to a process for monitoring the flowrate and intensity of an electro-magnetic emission, particularly of very short wave-length, in the vicinity of visible light, such as a wave emission in the ultra-violet, for germicidal or bacteriostatic or atmosphere purifying purposes, characterized in that a first and a second sensor are exposed to the radiations to be monitored, each sensor constituted by a transducer, particularly of the photovoltaic type, while a series of filters is interposed in front of said sensors, such that a first sensor is rendered exclusively sensitive to the radiations of the wave-length to be monitored, while the second sensor is rendered insensitive to said radiations, the currents issued by each of these transducers are permanently compared, the differential between the two currents being proportional to the intensity of the radiation monitored, which makes it possible to display this intensity. The invention also relates to a device for carrying out this process.