How does ultraviolet light sterilize? How to choose ultraviolet sterilization lamp?

After the outbreak of new coronavirus pneumonia, many families began to pay attention to sterilization and disinfection.

Some time ago, there was a rumors on the Internet: grab masks on the first day, instant noodles on the second day, alcohol on the third day, goggles on the fourth day, UV germicidal lamps on the fifth day, gloves on the sixth day, and double yellow on the seventh day.

I don't know if Shuanghuanglian is useful, but UV germicidal lamps are really useful.

Since the outbreak of the epidemic, many lighting companies have made concerted efforts to donate a lot of money and materials to Hubei, especially ultraviolet sterilization lamps. One of the world's leaders in special light source industry, Heraeus Special Light Sources in Germany has also assisted nearly 1,000 sets of ultraviolet disinfection lamps in Huanggang, Hubei for disinfection and sterilization in frontline hospitals, hoping to help the epidemic prevention.

So how does ultraviolet light kill bacteria? How to choose ultraviolet sterilization lamp?

1.The principle of ultraviolet disinfection

Ultraviolet light is a light wave that is invisible to the naked eye. It exists outside the violet end of the visible spectrum, so it is called ultraviolet light. Ultraviolet rays are a stream of unconnected particles, and each ultraviolet photon with a wavelength of 253.7 nm has an energy of 4.9 eV.

When ultraviolet rays are irradiated to microorganisms, energy transmission and accumulation occur, and the accumulation results in the inactivation of microorganisms, thereby achieving the purpose of disinfection. When bacteria and viruses absorb more than 3600 ~ 65000 uW / cm2, they have a strong destructive effect on the DNA and RNA of bacteria and viruses. Eliminate bacteria and viruses, and achieve the effect of disinfection and sterilization.

On the one hand, ultraviolet light can mutate nucleic acids, hinder their replication, transcription blockade and protein synthesis; on the other hand, the generation of free radicals can cause photoionization, which leads to the death of bacteria.

Some time ago, the National Health Commission and the State Administration of Traditional Chinese Medicine announced the "New Coronavirus Infection Pneumonia Diagnosis and Treatment Program (Trial Version 4)." The new version of the treatment plan states that the virus is sensitive to ultraviolet light and heat.

In this regard, Heraeus technical experts further introduced that when the cumulative ultraviolet dose received by most bacteria and viruses reaches 20mJ, the inactivation rate can be as high as 99%. 253.7nm ultraviolet light can effectively destroy the genetic material (DNA or RNA) of microorganisms, so that bacteria and viruses cannot complete the replication and transcription of genetic material, thereby killing bacterial pathogens and eliminating the source of infection.

The killing effect of ultraviolet radiation on bacteria and viruses has been verified on common bacteria and viruses: bacteria such as Mycobacterium tuberculosis (mycobacterium), Vibrio cholerae, Pseudomonas, Salmonella, intestinal fever bacteria, Typhi Bacillus, Shigella, Staphylococcus, Streptococcus, Escherichia coli; viruses such as influenza virus, poliovirus, rotavirus, tobacco leaf virus, hepatitis B virus; mold spores such as soft spores, penicillin Fungi, Toxigenic Penicillium, Penicillium and other fungi; Algae such as Paramecium, Chlorella, Protozoa. Therefore, ultraviolet radiation is a broad-spectrum sterilization method.

2. Can UV germicidal lamps kill coronavirus?

There are many types of coronaviruses, viruses that cause the common cold, SARS virus (SARS-CoV) that caused 2003, and the new 2019 coronavirus (COVID-19) found this time are all coronaviruses. Strength and clinical manifestations are also different. The COVID-19 discovered this time is the seventh coronavirus known to infect humans.

Viruses are sensitive to ultraviolet light and heat. As mentioned above, ultraviolet radiation is based on the broad-spectrum killing effect of viruses based on the destruction of nucleic acids. During the SARS period in 2003, studies also showed that ultraviolet radiation has confirmed the killing effect of SARS coronavirus in vitro The new coronavirus, as a (corona) virus, can theoretically be killed by ultraviolet radiation.

3. How long does it take to sterilize the virus?

The factor that needs to be considered in killing the virus is not so much the time, but the UV dose required. The ultraviolet radiation received by bacteria and viruses can be effectively killed only when they reach a certain dose.

The following is a list of the UV dose required for microorganisms with different structures to achieve an inactivation rate of 99.9%:

Note: 1mJ = 1000μW * s

In addition, the dose of ultraviolet radiation that can kill the virus is related to the following factors:

1. The total amount of ultraviolet radiation depends on the radiation time and radiation intensity;

2. The in vitro environmental conditions the virus is in, including the ambient temperature and humidity;

3. Penetration of viruses and attachments in vitro and ultraviolet radiation.

Taking the Heraeus 50W low-pressure ultraviolet sterilization lamp for indoor still air sterilization as an example, it is generally believed that the ultraviolet illuminance is very low at a distance of more than 2 meters from the surface of the ultraviolet lamp tube, and its sterilization efficiency is negligible.

Picture: Heraeus low-pressure ultraviolet sterilization lamp

The ultraviolet sterilization lamp has an effective life of 9000 hours, can be wall-mounted or hoisted, and is suitable for indoor places that require sterilization, such as hospitals, schools, families, and public toilets.

Single opening time exceeds 30 minutes, can sterilize the air, and sterilize the surface of the irradiated object. (Note: After the UV lamp is turned on, personnel must leave.)

How to choose ultraviolet germicidal lamp?

It is known that a sufficient UV dose is required to kill viruses, so the irradiation intensity (mw / c㎡) and effective service life (h) of UV lamps are the two most important factors to consider when selecting UV lamps. The effective service life mentioned here refers to the time when the ultraviolet decay to a certain extent can not be effectively sterilized, rather than the ultraviolet lamp is not on.

Let me talk about the irradiation intensity

There are three main factors that affect the irradiation intensity of the ultraviolet lamp, which are the total power of the ultraviolet lamp, the lamp tube material and the supporting power supply. Here it is emphasized that the ultraviolet transmittance of the quartz glass material is higher than 85%, which is superior to the high boron glass material It is more helpful to increase the irradiation intensity of the ultraviolet lamp, as shown in the following figure:

Let's talk about the effective life

The material that affects the effective life of the ultraviolet lamp mainly includes the material of the ultraviolet lamp, the key production process and the supporting power supply. Here I would like to recommend Heraeus's unique long-life coating technology, which can effectively help delay UV attenuation.

Look at an experimental comparison chart:

Figure: The same UV lamp produced by Heraeus. The left half uses long-life materials, while the right half only uses high-purity quartz and does not use long-life materials.

From the picture of this UV lamp after 10,000 hours of testing, we can see that there is almost no change in the left half, the attenuation of the ultraviolet intensity is less than 10%, and the right half is obviously yellow. above 50.

Expert interpretation

Professor Fang Daoxu of Fudan University commented: UV disinfection has a great role in preventing new pneumonia, and the quality of the ultraviolet light used is very important. Heraeus UV lamps are the best quality UV disinfection light sources in the world. Its UV output maintenance rate can still reach more than 90% after thousands of hours of operation. The UV output maintenance rate of domestic UV lamps is much lower because of the poor quality of quartz glass. To achieve a maintenance rate of more than 90%, a high-purity nano-alumina protective film must be coated on the inner surface of the quartz glass tube. The research work of many domestic enterprises producing ultraviolet germicidal lamps proves this point.

Zhang Shanduan, deputy director of the Institute of Electric Light Sources of Fudan University: supporting ballast, Heraeus ultraviolet sterilization lamp can achieve 10% light attenuation within 10,000 hours.

Former Deputy Director of Jiangsu Provincial Lighting Society and Association, Yan Ci: Heraeus ultraviolet sterilization lamps during the SARS period performed very well, and the product quality was good!

It is understood that Heraeus has designed different products such as high-temperature amalgam, low-temperature amalgam and liquid mercury according to the different luminous efficiency characteristics of mercury with temperature to improve the UV conversion efficiency of the lamp at different temperatures. Under working conditions, to achieve maximum UV output.