The principle of disinfection by the UVC lamp is to use the appropriate wavelength of UV light to destroy the DNA (deoxyribonucleic acid) or RNA (ribonucleic acid) molecular structure of microbial cells, resulting in growth cell death and (or) regenerative cell death, to achieve the effect of disinfection.
UV light can kill various microorganisms, including bacterial propagules, spores, bacilli, viruses, rickettsiae and mycoplasma.
To prevent the spread of diseases, many chicken farms use UV lamps for disinfection, and to achieve the desired disinfection, the correct use of UVC lamps is required. and methods to check the germicidal effect of UVC lamps.
Let’s dive right in now, and you can click on the question that interest you,
1 Irradiation intensity and dose
1) Illumination intensity
The irradiation intensity of UV lamps is often expressed in terms of the number of microwatts per square centimeter irradiated per second: 1 μW-s/cm².
2) Irradiation dose
The irradiation dose is expressed as the product of the irradiation intensity of the UV source used and the irradiation time.
It is also expressed in μW-s/cm². For example, if a 15W UV lamp is irradiated at 38 μW-s/cm² at a distance of 1 m from the lamp, the dose received at one meter is 4560 (38×2×60) μW-s/cm² after 2 min of irradiation.
2 Germicidal ability and irradiation intensity
The germicidal ability of UVC lamps is closely related to the intensity of exposure. The intensity of UV lamp irradiation is inversely proportional to the distance to the square, the closer the distance, the stronger the germicidal power, and generally the better quality of the UV lamp, up to 120μW-s/cm² or more at 1 m from the center of the lamp vertically.
3 Illumination measurement and time
Different types of microorganisms have different sensitivities to UV light, and when using UV light for disinfection, the dose of irradiation required to kill the target microorganism must be used.
A dose of 20,000 μW-s/cm² should be used to kill general bacterial propagules, and between bacterial spores, fungal spores are more resistant than bacterial spores. When the target microorganism for disinfection is unknown or when multiple microorganisms are to be killed, the irradiation dose should not be lower than 100000 μW-s/cm².
This is because the irradiation dose is the product of the irradiation intensity of the UV light source used and the irradiation time. Therefore, the time required to be irradiated can be calculated from the intensity of the UV light source. For example, if a 70μW/cm² UV lamp is used to disinfect a surface and the dose is 100000μW-s/cm², then the time required for irradiation is: 100000μW-s/cm² divided by 70μW/cm² = 1429s = 24 min.
4 Usage and requirements
(1) For disinfection of object surfaces, the UV intensity of the irradiated surface should not be less than 70μW/cm² and the irradiation time should not be less than 25 min, and the irradiation time can be reduced if the intensity of the UV light source used is high.
(2) For disinfection of air in the barn, regardless of whether direct or indirect irradiation is used, the natural bacteria in the air must be reduced by more than 90% after disinfection. When using suspended UV lamps in the barn for disinfection, the power of the lamp should be at least 1W per cubic meter on average. Generally, one 30W UV lamp should be installed in every 10 square meters of the barn. The irradiation time should be 40-120 min each time, and then ventilation for 1h to reduce the ozone content in the air.
(3) Requirements for the use of UV lamps. Ultraviolet radiation is low in energy and weak in penetration, and can only kill directly irradiated microorganisms, therefore, the disinfection site must be fully exposed to UV light. When disinfecting porous surfaces such as textiles with UV light, the irradiation time should be extended so that both sides are irradiated. The appropriate temperature range for UV disinfection is 20-40°C. Too high or too low a temperature will affect the disinfection effect, and the irradiation time can be extended appropriately. When using UV to kill microorganisms protected by organic matter, the irradiation dose should be increased.
5 UVC lamp germicidal effect inspection
The germicidal effect of the UV lamp can be measured biologically, not only to check the germicidal effect of the UV lamp but also to check whether the intensity of the UV lamp has been reduced or failed during the use of the lamp. (1) Place the nutrient agar plate under the UV lamp (1 m from the center of the lamp vertically) and irradiate it for a certain period of time (calculate the irradiation time based on the dose required by the microorganism being irradiated and the intensity of the UV light source), then place the agar plate in a 37 °C incubator for 24h and observe the bacterial growth. If it is close to the control group (not irradiated plate), it means that the UV lamp has failed. (2) Inoculate the 24h broth culture of the bacteria to be examined with deep agar tubes that have been dissolved and cooled to 50 °C. After mixing, pour each tube into different sterilized dishes separately, and after the agar has solidified, remove the lid of the dishes and place them under the UV lamp for different times (5, 10, 20, 40, 60 min), take out one dish each, cover the lid of the dishes and place them in the incubator at 37 °C. The growth of the bacteria was observed for 24-72h to determine the killing effect of UV light on the bacteria or the resistance of the bacteria to UV light.
The wavelength of ultraviolet light is shorter than visible light and cannot be seen by the naked eye. The wavelength of the strong germicidal power is 250~265 nm, while the wavelength of ozone formation is 840 nm. Therefore, the germicidal power of UV can not be judged by the intensity of the orchid light emitted by the UV lamp and the intensity of the ozone smell alone. If you have the conditions, you should measure the intensity of the lamp regularly, and if not, you should establish a registration system for use, and record the time of use day by day to determine whether the use period has been reached. To determine whether to reach the use period. When the use of time exceeds 1000 h should be replaced. Although the lamp at this time still will light up, the surface also looks very normal, but in fact, The disinfection effect is no longer reliable. The average life span of the violet lamp is generally 3000~4000h.
References
[1] The use of light therapy in veterinary clinical practice[J]. Sun Lixia. Information on animal husbandry and veterinary science and technology. 2020(11)
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