Why does UVC LED disinfection work best at a wavelength of 254 nm?
uvb is a kind of lamp that imitates sunlight. In the case of no sunlight, this lamp can be used instead
UV Lamp - Ultraviolet Germicidal Lamp
Classification of UV rays:
According to different biological effects, ultraviolet rays are divided into four bands according to wavelength:
UVA band, wavelength 320 ~ 400nm, also known as long-wave dark spot effect ultraviolet. It has strong penetrating power and can penetrate most transparent glass and plastics. More than 98% of the long-wave ultraviolet rays contained in sunlight can penetrate the ozone layer and cloud layer to reach the earth's surface. UVA can directly reach the dermis of the skin, destroy elastic fibers and collagen fibers, and tan our skin. The UVA ultraviolet rays with wavelength of 360nm are in line with the phototaxis response curve of insects, and can be used to make trap lights. UVA ultraviolet rays with wavelengths of 300-420nm can pass through special colored glass lamps that completely cut off visible light, and only radiate near-ultraviolet light centered at 365nm, which can be used in ore identification, stage decoration, banknote inspection and other places.
UVB band, wavelength 275 ~ 320nm, also known as medium wave erythema effect ultraviolet. Medium penetrating power, its shorter wavelength part will be absorbed by transparent glass, most of the medium-wave ultraviolet rays contained in sunlight are absorbed by the ozone layer, and only less than 2% can reach the earth's surface, which is especially strong in summer and afternoon. UVB ultraviolet rays have an erythematous effect on the human body, which can promote the metabolism of minerals and the formation of vitamin D in the body, but long-term or excessive exposure will tan the skin and cause redness and peeling. Ultraviolet health lamps and plant growth lamps are made of special transparent violet glass (which does not transmit light below 254nm) and phosphors with a peak value around 300nm.
UVC band, wavelength 200 ~ 275nm, also known as short-wave sterilization ultraviolet. It has the weakest penetrating ability and cannot penetrate most transparent glass and plastics. The short-wave ultraviolet rays contained in sunlight are almost completely absorbed by the ozone layer. Short-wave ultraviolet rays are very harmful to the human body. Short-term exposure can burn the skin. Long-term or high-intensity exposure can also cause skin cancer. Ultraviolet germicidal lamps emit UVC short-wave ultraviolet rays.
UVD band, wavelength 100 ~ 200nm, also known as vacuum ultraviolet.
The sterilization principle of ultraviolet light
Ultraviolet sterilization is to destroy and change the DNA (deoxyribonucleic acid) structure of microorganisms through the irradiation of ultraviolet rays, so that the bacteria immediately die or cannot reproduce, so as to achieve the purpose of sterilization. What really has a bactericidal effect is UVC ultraviolet rays, because the C-band ultraviolet rays are easily absorbed by the DNA of the organism, especially the ultraviolet rays around 253.7nm.
Ultraviolet sterilization is a pure physical disinfection method, which has the advantages of simplicity and convenience, broad-spectrum efficiency, no secondary pollution, easy management and automation. expand.
The structure of ultraviolet germicidal lamp
Ultraviolet germicidal lamp (UV lamp) is actually a low-pressure mercury lamp. Like ordinary fluorescent lamps, it emits ultraviolet rays after being excited by low-pressure mercury vapor (<10-2Pa). The difference is that the lamp tube of the fluorescent lamp is made of ordinary glass, and the 254nm ultraviolet rays cannot penetrate, and can only be absorbed by the fluorescent powder on the inner wall of the lamp tube to excite visible light. If you change the composition and proportions of the phosphor, it can emit different colors of light that we usually see. Generally, the lamps of germicidal lamps are made of quartz glass, because quartz glass has a high transmittance of ultraviolet rays in various bands, reaching 80%-90%, which is the best material for germicidal lamps.
Germicidal lamps have several structures such as hot cathode low pressure mercury vapor discharge lamps and cold cathode low pressure mercury vapor discharge lamps, which can be divided into various types according to appearance and power.
Quartz glass is very different from ordinary glass in performance, mainly due to the difference in thermal expansion coefficient, and generally cannot be sealed with aluminum caps.
UV germicidal lamp tube
Due to the difference in cost and use, high borax glass tubes with UV transmittance < 50% are also used instead of quartz glass. The production process of high boron glass is the same as that of energy-saving lamps, so the cost is very low, but its performance is far less than that of quartz germicidal lamps, and its sterilization effect is quite different.
The ultraviolet light intensity of high-boron lamps is easily attenuated, and the ultraviolet light intensity drops significantly to 50%-70% of the initial value after hundreds of hours of lighting. After the quartz lamp is ignited for 2000-3000 hours, the ultraviolet intensity is only reduced to 80%-70% of the initial time, and the light decay degree is far less than that of the high-boron lamp.
It is also a kind of ordinary glass with higher ultraviolet light transmission, which is much higher than high boron glass and slightly lower than quartz glass. However, the light decay is larger than that of the quartz germicidal lamp, and it cannot produce ozone. The tube on a germicidal lamp produced by Philips is made of this glass.
Types of UV germicidal lamps
The emitting spectral lines of ultraviolet germicidal lamps are mainly 254nm and 185nm. 254nm ultraviolet rays kill bacteria by irradiating the DNA of microorganisms, and 185nm ultraviolet rays can turn O2 in the air into O3 (ozone). Ozone has a strong oxidizing effect and can effectively kill bacteria. Propagation and disinfection along a straight line have the disadvantage of dead corners.
When quartz glass is refined, if a sufficient amount of titanium (Ti) element is added, the ultraviolet rays passing through it can be cut off below 200nm, and it has basically no effect on the transmission of 254nm ultraviolet rays. Appropriate control of the amount of titanium added can effectively control the escaping amount of 185nm ultraviolet rays. According to this feature, we can make three kinds of ultraviolet germicidal lamps, such as low ozone (no ozone), ozone and high ozone.
Application of UV germicidal lamps
1. Each microorganism has its specific ultraviolet ray killing and death dose standard, and its dose is the product of irradiation intensity and irradiation time (bactericidal dose=irradiation intensity·irradiation time/K=I·t), that is, the irradiation dose of ultraviolet rays. It depends on the intensity of ultraviolet rays and the length of irradiation time. The effect of high-intensity short-time irradiation and low-intensity long-time irradiation is the same.
2. Quartz lamps will gradually age after being used for a period of time, and the intensity of ultraviolet radiation will decline. In order to achieve the effect of thorough disinfection, the irradiation intensity of quartz lamps should be checked regularly, and if the intensity is found to be insufficient, it should be replaced immediately.
3. Ultraviolet rays can only travel in a straight line, and the penetrating ability is weak. Any paper, lead glass, or plastic will greatly reduce the irradiation intensity. Therefore, when sterilizing, try to fully expose the sterilized part to ultraviolet rays, and wipe the lamp tube regularly to avoid affecting the ultraviolet penetration rate and irradiation intensity.
4. Ultraviolet rays can cause great harm to the skin of the human body. Do not use UV lamps in places where there are people, and do not look directly at the ignited lamps. Because short-wave ultraviolet rays cannot pass through ordinary glass, wearing glasses can be avoided. Eye damage.
5. Ozone lamps are generally not used in places where there are personnel activities, because ozone will promote the coagulation of human hemoglobin, resulting in insufficient oxygen supply to the human body, dizziness, nausea, and affecting health, especially when the ozone concentration reaches > 0.3ppm (mg/m2), it will cause serious harm to the human body.
6. The purple-blue light in the low-pressure discharge lamp is the mercury vapor pressure. Although the intensity of the mercury vapor pressure is still related to the ultraviolet light, it does not directly represent the intensity of the ultraviolet light, which means that the intensity of the ultraviolet light cannot be used by the naked eye. to judge.
7. Lamps and reflectors can ensure the concentration of ultraviolet energy, and can avoid damage to the staff. The reflector must be made of materials that attract less and reflect more to 253.7nm ultraviolet materials. The surface oxidation and polishing of aluminum has the highest reflection coefficient for short-wave ultraviolet rays, so the reflector system of general ultraviolet lamps is made of aluminum.
Problems with UV germicidal lamps
1. The process is special, the manufacturing is difficult, and the price is high. Due to the special properties of quartz glass, the production of germicidal lamps cannot be scaled, resulting in high cost of quartz germicidal lamps and hindering its further promotion and application.
2. The light decay is large and the life is not long. After the ultraviolet germicidal lamp is lit for hundreds of hours, its ultraviolet light intensity attenuates rapidly, up to 30%, and the sterilization effect is greatly weakened. In addition, the cathode damage caused by processing also affects the life of the UV germicidal lamp. Since the light decay of ultraviolet germicidal lamps and fluorescent lamps are not identical in mechanism, this problem still needs to be solved by all parties.
3. Due to the different filament and cathode materials, UV lamps with the same power as T8 and T5 fluorescent lamps cannot be driven by the same ballast.
