Ultraviolet germicidal lamps are actually low-pressure mercury lamps. The low-pressure mercury lamp is excited by the lower mercury vapor pressure (<10-2Pa) to emit ultraviolet light. At 25 °C, there are two main spectral lines: one is 253.7nm wavelength; the other is 184.9nm wavelength, which is Both are ultraviolet rays invisible to the naked eye.

At present, only artificial mercury (alloy) light sources can output sufficient UVC intensity for engineering disinfection. The ultraviolet germicidal lamp tube is made of quartz glass. The mercury lamp is divided into three types according to the difference of mercury vapor pressure in the lamp after lighting and the difference of ultraviolet output intensity: low-pressure low-intensity mercury lamp, medium-pressure high-intensity mercury lamp lamps and low pressure high intensity mercury lamps. The bactericidal effect is determined by the irradiation dose received by microorganisms, and at the same time, it is also affected by the output energy of ultraviolet rays, which is related to the type of lamp, light intensity and use time. As the lamp ages, it will lose 30%-50% of its intensity. . The ultraviolet irradiation dose refers to the amount of ultraviolet rays of a specific wavelength required to achieve a certain bacterial inactivation rate: irradiation dose (J/m2) = irradiation time (s) × UVC intensity (W/m2) The greater the irradiation dose, the better the disinfection efficiency. Due to the size requirements of the equipment, the general irradiation time is only a few seconds. Therefore, the UVC output intensity of the lamp has become the most important parameter to measure the performance of the ultraviolet light disinfection equipment. In urban sewage disinfection, the average irradiation dose is generally above 300 J/m2. Below this value, the phenomenon of photoresurrection may occur, that is, the bacteria cannot be completely killed, and when they flow out of the channel and receive visible light irradiation, they will be revived again, reducing the sterilization effect. The higher the requirement for sterilization efficiency, the larger the required irradiation dose. The main factor affecting the exposure of microorganisms to sufficient ultraviolet light irradiation dose is the transmittance (at 254 nm). When the UVC output intensity and irradiation time are constant, the change of light transmittance will cause the actual dose of microorganisms to change.

Most UV installations use traditional low-pressure UV lamp technology, and some large water plants use low-pressure high-intensity UV lamp systems and medium-pressure high-intensity UV lamp systems, which may reduce the number of lamps by more than 90% due to the generation of high-intensity The floor space is reduced, installation and maintenance costs are saved, and the ultraviolet disinfection method is also applicable to the effluent with poor water quality.