UV disinfection lights really work?

In the beginning of 2020, a sudden new corona virus (recently Zhong Nanshan team published a paper called 2019-nCoV ARD, the new coronavirus acute respiratory disease) swept the country at an unprecedented rate, causing anxiety, people snapped up masks, disinfectant water, alcohol, double yellow even, and of course, ultraviolet disinfection to kill according to the newly released “New Coronavirus Pneumonia Diagnostic Rapid Guide” wrote that 75% alcohol, ether, chloroform, formaldehyde, chlorinated disinfectant, peroxyacetic acid and ultraviolet light can inactivate the virus (17 years ago during the SARS period ultraviolet disinfection lamp also snapped up). Now many UV lamp enterprises in overtime production to support Wuhan, why upstream material manufacturers are in short supply, limited production, can only come slowly.

UV Lamp

Probably many ordinary consumers feel that the home does not use UV germicidal lamps, a bit big material and small use. In fact, we live in an environment where bacteria are everywhere, in the air, in the corner of the kitchen, on the toilet, on the desktop, on our phones, on our clothes… all are viral bacteria that we cannot see with our naked eyes. Regularly disinfecting with a UV lamp is still necessary, rather than spraying around the corner with alcohol/disinfectant water and scrubbing it repeatedly. It’s also said to prevent colds, after all, most of the time we get colds from viral bacterial invasion.

OSRAM once conducted a market research and found that the attendance rate of children in kindergartens with germicidal UV lamps increased by 1% to 5%. Cross-infection is a frequent occurrence. When a child gets sick, parents take leave and go to the hospital, it takes a lot of energy and money. PS: Many UV germicidal lamps on Taobao boast that they can kill the mites in the quilt and pillow, so please note that UV germicidal lamps cannot get rid of mites. What mites fear is dehydration at high temperatures, so it’s better to bake the mites in the sun and suck them away with a big suction Dyson

Ultraviolet light (UV) is classified as a wavelength between 100 and 400 nm in the spectrum, between X-ray and visible light. Ultraviolet light can be divided into UVA, UVB, UVC and UVD depending on the wavelength.

UV Lamp

I will not say anything about the detailed expansion of applications such as the various wavelengths of ultraviolet light, after all, there is no direct connection with our daily family life, I will simply introduce the UV classification characteristics.

UVA

Long-wave ultraviolet light, with a wavelength of 320 to 400 nanometers, is the most penetrating, so UVA ultraviolet light from the sun can penetrate the ozone layer and clouds directly to the Earth’s surface.

UVA can reach the dermis of the skin and directly damage the cells, which can tan your skin and make it wrinkly. That’s why it’s time for the girls to go out and put on more sunscreen.

UVB

Medium-wave ultraviolet light, with wavelengths between 280 and 320 nm, is mostly absorbed by the ozone layer, with only about 2% to 10% reaching the surface.

It promotes mineral metabolism and vitamin D formation in the body, which is why we often talk about vitamin D supplementation from proper sun exposure. But with too much sun, your skin will become red, swollen and sore and molt.

UVC

Short-wave ultraviolet light, with a wavelength of 200 to 280 nm, is almost completely absorbed by the ozone layer and has a weak penetration ability, unable to penetrate ordinary glass and plastic products.

The germicidal lamp uses UVC shortwave UV light.

Although the penetrating power is weak, it is very harmful to the human body and should not be directly irradiated.

UVD vacuum ultraviolet light, with wavelengths of 100 to 200 nanometers and very little penetration, oxidizes oxygen in the air to ozone. I believe many post-80’s children should have seen the movie “The Atmosphere Disappears”, in which Ge You and Lv Liping played, which can be said to be the earliest science fiction disaster movie in China. The story is of a crisis caused by excessive ultraviolet rays penetrating the Earth due to the hole in the ozone layer. The dog sacrifice scene at the end really made me cry a lot. Heck, why can’t China make movies like this now?

The working principle of ultraviolet sterilization is to use the bactericidal effect of UVC ultraviolet light (mainly 240 nm ~ 280 nm) to destroy the DNA (DNA) and RNA (ribonucleic acid) molecular structure of microbial cells, causing the death of growing cells and/or regenerative cells, to achieve the effect of disinfection. Don’t worry about what kind of germs it can kill, it can kill most of the bacterial viruses including the new coronavirus (you don’t know what kind of bacterial viruses exist in your home, it seems that no instrument can detect this in real time, and some germs really can’t kill), in any case, no matter the good or the bad, it’s a kill.

UV Lamp

All coronaviruses are single-stranded positive-stranded RNA viruses.

So how do UV germicidal lamps emit UVC rays?

There are currently two main sources of UV germicidal lamps – gas discharge sources and solid state sources. Gas discharge sources are mainly low pressure mercury lamps. The principle of luminescence is the same as that of our previous fluorescent lamps, which excite the mercury atoms in the lamp, and the low-pressure mercury vapour mainly produces 254nm UVC (30%-60% radiation efficiency) and 185nm UVD (5%-15% radiation efficiency).

UV lamp

It is said above that UVC ultraviolet disinfection is the most effective, but the ultraviolet light can only spread in a straight line, the penetration is weak, so there is a blocked disinfection dead corner.185nm UVD ultraviolet light itself does not have a strong and effective physical disinfection, but it can decompose the oxygen in the air combined to produce ozone, ozone has a strong oxidation effect, can with the air flow to all corners, thoroughly disinfection (biochemical oxidation disinfection).

But high levels of ozone are harmful and can cause chest tightness and dizziness. Therefore, if you purchase the ozone type UV lamp, you need to open the window for 30-60 minutes after sterilization before moving in.

The advantages of low-pressure mercury lamps are that the technology is mature and the sterilization efficiency is high, but the large size and a small amount of mercury contamination (normally it is better to put it in a place where children can not touch it, it will not be good to break it).

Gas discharge light source and pulsed xenon lamp, the use of thermal shock and partial ultraviolet light to sterilize, sterilization efficiency is higher than low-pressure mercury lamp, but the mature technology is mastered by foreign manufacturers, there are technical barriers to the cost is also high, so I will not extend the discussion here (civil field is rarely used).

UV Lamp

A solid-state light source is a UV-LED light source, and the radiation efficiency of UV-LED is several orders of magnitude lower than that of a low-pressure mercury lamp, which can only reach about 3% (in this case, imported chips, domestic chips are less than 2%). Costs are also currently very high, and to achieve the same unit radiation dose is much more expensive than low-pressure mercury lamps. Some companies are already using UV-LED in water purifiers, air conditioners, air purifiers, it is believed that in the future, with the decline of technology and cost, will be widely used in civilian areas.

Because LED light sources can be made very small, they are currently used in small object sterilizers. We buy online what kind of mobile phone / mask / underwear / contact lens disinfection box, we have to carefully distinguish what light source, if the LED light source is still very cheap, then we have to pay attention to the possible effective germicidal ultraviolet intensity is very small, or no germicidal disinfection effect PS: expensive price may also have no effect, take you as a leek just. After all, you don’t spend $10,000+ on a UV intensity tester to test.

How to choose a UV lamp

At present, most of the UV disinfection lamps sold in the market are still using low-pressure mercury lamps with mature technology.

Low-pressure mercury lamps are available in two main types of glass – quartz glass and high boron glass. Just say that the ultraviolet transmittance and radiation intensity of high boron glass are lower than quartz glass, buy domestic brands of ultraviolet germicidal lamps (tubes) must choose quartz glass tubes.

I mentioned above that UVC has weak UV penetration and will not penetrate normal glass. General consumers can not distinguish the difference between quartz glass, high boron glass and ordinary glass, so we buy ultraviolet disinfection germicidal lamp (tube), do not covet the cheap choice of miscellaneous goods, buy back thinking that the light glow is able to sterilize the disinfection, in fact, may have no effect at all, wasted silver. The market is mixed, quartz glass tube and ordinary glass tube price difference is quite large, resulting in a lot of lucrative manufacturers produce inferior products (function boasted also oddly enough) cheat consumers. Be sure to choose the big brands of regular manufacturers such as: Philips, Panasonic, Osram, Guangming Yuan, Shelite, etc.

How much power to choose? Our ordinary consumers choose the ultraviolet lamp, then, do not need high standard germicidal requirements, only a fixed power ultraviolet germicidal lamp is good to have a rough calculation formula: 1 cubic meter configuration 1.5W ultraviolet lamp. For example, if your bedroom is 15 square meters and your floor is 3 meters high, then the power of the UV lamp is 15×3×1.5=67.5W, which means you need to buy a 60W UV germicidal lamp. In the medical / school / factory, because the space is relatively large, and there is a high germicidal requirements, need multiple ultraviolet lamp hanging up evenly distributed, there is also a reference formula, probably understand the good n=0.05v/hn — ultraviolet germicidal lamp number, according to a 30w calculation h — germicidal lamp to the ceiling distance (m) v — room volume, cubic meters f — lamp efficiency, generally take 0.8

Choosing Ozone or No Ozone? First and foremost, again, whether ozonated or not, UV disinfection lamps are harmful to the eyes and skin and need to be operated safely. Just now it was also said that ozone can be thoroughly sterilized through air flow to some dead ends, eliminate odors, generally used in the kitchen, bathroom. But ozone is harmful to the human body, and rubber, iron products, plastic products and other corrosive, so the best time to sterilize the valuables put away, after disinfection room window ventilation 30-60 minutes (such as can also smell the pungent smell, continue to ventilate) so choose to have ozone or no ozone, depending on their family needs to decide!

How long does it take to sterilize?

There is a very long table of UV germicidal doses on the Internet that states how much UV irradiation is needed for each bacterial virus to be killed and how long it takes to kill the corresponding germs can be deduced from the intensity of the UV light.

UV Lamp

For a simple example, an influenza virus with 99% inactivation rate requires a UV irradiation dose of 6600 µWs/cm2 (actually the dose is in mJ/cm2, the µWs/cm2 on this side is converted for time)

A new 30W ultraviolet lamp with an intensity of 100 µW/c㎡ at a distance of 1 meter or more, with a minimum insurance value of 90 µW/c㎡, the time to kill the flu virus is 6600÷90=73.3s, or 1 minute and 13 seconds.

I won’t put it away, and you won’t look at it, and we don’t know what germs are present in the house. This form should be for those special professional places for targeted sterilization, so as to accurately control the irradiation time and save electricity costs.

Take a 30W UV lamp at a vertical distance of 1 meter with an irradiation intensity of 90~100μW/c㎡ for example, irradiate for 30~60 minutes.

How long will it take to kill the new coronavirus?

The latest guidelines issued by the CDC also only say that “ultraviolet light can inactivate novel coronaviruses,” not how long it will take to do so. No accurate experimental data has been seen to prove exactly how much UV radiation dose can kill the new coronavirus.

A 2003 study by Dong Xiaoping, an expert at the Institute of Virus Prevention and Control of the Chinese Center for Disease Control and Prevention, reported that the SARS coronavirus could be killed in 60 minutes by irradiating the SARS coronavirus with UVC at an intensity greater than 90 μW/cm² (note that this is 60 minutes, not 30 minutes as we see in the daily news). Exactly how much mJ/cm2 dose is needed I will not say, the results of domestic and foreign studies are different, for fear of controversy.

How often do you need to change the lamp? above mentioned that the radiation intensity of ultraviolet lamps will be attenuated, different brands are different, and the quality of the lamp, ballast matching / good, frequency of use, switching times, the use of the environment and post-maintenance have a relationship. In addition to the purchase of expensive ultraviolet intensity measuring instrument such as this tool, ordinary consumers can spend more than 20 yuan on Taobao to buy the “four-ring brand ultraviolet intensity indicator card” test, although the accuracy is not high, but for daily household life lamp replacement is a simple and cheap test method. The lamps here are mainly for low-pressure mercury lamps above 30W, but small wattage lamps have no reference value. Wear long-sleeved clothes, a good face shield and gloves for the test. I can only suggest that if your family doesn’t use it very often, the insurance period, can be changed once a year or two. (Professionals are also welcome to leave better suggestions.)

How to safely regulate the use?

First of all, pay attention to the ambient temperature, too high or too low will affect the UV radiation intensity and thus the bactericidal effect. Ultraviolet radiation is most intense and stable at room temperature between 20 and 40°C. Therefore, temperatures below 20°C or above 40°C require an appropriate extension of the UV exposure time. The highest rate of killing of germs by ultraviolet light is found when the humidity is 55% to 60%. When the humidity exceeds 60%, the penetration of ultraviolet light decreases and the bactericidal effect is reduced by 20% to 30%. It’s best to use it when the weather is nice and dry indoors, and don’t disinfect it with a UV lamp as soon as you’ve finished mopping the floor with a wet mop or mopping the table. Don’t look directly into the light-emitting lamp (don’t be nervous if you wear glasses, the lenses block UVC rays) and don’t leave your skin exposed for long periods of time under a lighted UV lamp. During disinfection, doors and windows must be closed, people and pets must leave the disinfected area, and plants and valuable leather goods should preferably be moved to places where they cannot be exposed to ultraviolet light or covered with a cloth. If you’re on a budget, just buy the one with smart sensor or remote control and be safe.