A control circuit for controlling a UV light source configured to emit UV light into a purifying chamber of a device for purifying a fluid, the control circuit comprising: a driver configured to provide the UV light source with a drive current; a fluid flow sensor configured to determine whether a flow of a fluid through the purifying chamber is present and generate a flow signal indicative thereof; a light sensor configured to measure radiant flux of light emitted from the UV light source before the light emitted from the UV light source has entered the purifying chamber and to generate a radiant flux signal comprising data pertaining to the measured radiant flux; a memory comprising a reference radiant flux; and a processor configured to: upon the flow signal being indicative of presence of flow of fluid through the purifying chamber, activate the UV light source; during the UV light source being activated due to presence of flow of fluid through the purifying chamber, determine the drive current for the driver based on the measured radiant flux comprised in the radiant flux signal and the reference radiant flux; and upon the flow signal being indicative of non-presence of flow of fluid through the purifying chamber, instruct the driver to apply a drive current below a threshold to the UV-light source, wherein the threshold is set so that the radiant flux of UV-light emitted from the UV light source is ≤ 5% of a maximum radiant flux of UV-light emitted from the UV light source. a driver configured to provide the UV light source with a drive current; a fluid flow sensor configured to determine whether a flow of a fluid through the purifying chamber is present and generate a flow signal indicative thereof; a light sensor configured to measure radiant flux of light emitted from the UV light source before the light emitted from the UV light source has entered the purifying chamber and to generate a radiant flux signal comprising data pertaining to the measured radiant flux; a memory comprising a reference radiant flux; and a processor configured to: upon the flow signal being indicative of presence of flow of fluid through the purifying chamber, activate the UV light source; during the UV light source being activated due to presence of flow of fluid through the purifying chamber, determine the drive current for the driver based on the measured radiant flux comprised in the radiant flux signal and the reference radiant flux; and upon the flow signal being indicative of non-presence of flow of fluid through the purifying chamber, instruct the driver to apply a drive current below a threshold to the UV-light source, wherein the threshold is set so that the radiant flux of UV-light emitted from the UV light source is ≤ 5% of a maximum radiant flux of UV-light emitted from the UV light source. upon the flow signal being indicative of presence of flow of fluid through the purifying chamber, activate the UV light source; during the UV light source being activated due to presence of flow of fluid through the purifying chamber, determine the drive current for the driver based on the measured radiant flux comprised in the radiant flux signal and the reference radiant flux; and upon the flow signal being indicative of non-presence of flow of fluid through the purifying chamber, instruct the driver to apply a drive current below a threshold to the UV-light source, wherein the threshold is set so that the radiant flux of UV-light emitted from the UV light source is ≤ 5% of a maximum radiant flux of UV-light emitted from the UV light source.