Ultraviolet disinfection belongs to physical disinfection method. Ultraviolet radiation can not kill microorganisms directly, but inactivate them by destroying their reproductive capacity. When microbes are exposed to ultraviolet radiation, their genetic material, nucleic acid DNA and RNA, is destroyed by a large amount of ultraviolet radiation, losing the ability to split and replicate, and eventually die naturally or be eliminated by the immune system, and lose its pathogenicity to the human body.

As shown in the figure electromagnetic spectrum, the human eye visible spectrum range is generally 400-700 nm, wavelength greater than 100 nm, less than 400 nm electromagnetic wave is called ultraviolet light. After the atomic or molecular outer electrons get energy, the excited state is moved to the excited state. The electrons can not stay in the excited state and move to the ground state. In this process, the energy is radiated in the form of photons, that is, ultraviolet.

According to the biological effects of ultraviolet radiation, ultraviolet radiation can be divided into four bands at wavelengths from high to low.

UV-A (400-315nm): also known as black light, has the longest wavelength and the lowest energy, occupying the largest share of ultraviolet light in nature. It can cause skin pigmentation to produce black spots, so it is also called black spot ultraviolet.

UV-B (315-280nm): it is the most destructive part of the ultraviolet light in nature, which causes sunburn and erythema, partly absorbed by the atmospheric ozone layer, and is also called the ultraviolet light of the erythema.

UV-C (280-200nm): all absorbed by the atmosphere, usually generated by artificial light sources. For sterilization, the wavelength is ultraviolet.

Vacuum ultraviolet (200-100nm): can not enter the atmosphere, exists in space.

As shown in the picture, we can see that the scope of the ultraviolet absorption spectrum of the genetic material nucleic acid DNA and RNA is 250-280nm. The traditional low pressure mercury lamp has two main lines of 254nm and 185nm. Therefore, when the ultraviolet light wavelength is 254nm, the nucleic acid has the maximum absorption of ultraviolet light, that is, the bactericidal effect is best.

With the heat of the third lighting revolution caused by the white light LED solid-state lighting, people gradually shifted the focus to the UV LED with high Al component III nitride as the structural material. UV LED has great application value in medical treatment, sterilization, printing, lighting, data storage, and secure communication. And compared with the traditional gas ultraviolet lamp such as mercury lamp and hernia lamp, UV LED has strong advantages.

The birth of ultraviolet light has led to the true application of ultraviolet light. Gas discharge light source is the main form of ultraviolet light source before the birth of deep ultraviolet LED. The spectral emission range of the gas discharge light source covers the ultraviolet region. The maximum efficiency is 60%, and the life span is 100-1000 hours.

The main source of gas discharge light is argon and mercury vapor. According to the pressure of mercury vapor in the lamp tube, mercury lamp is divided into low pressure, high pressure and super high pressure mercury lamp. Different low pressure mercury lamps can be divided into hot cathode low pressure mercury lamp and cold cathode low pressure mercury lamp according to the electrode. The hot cathode mercury lamp is an arc discharge lamp, and three yuan salt oxide is used as the cathode. The cold and hot cathode mercury lamp belongs to the glow discharge lamp, uses the pure metal as the cathode.