👵🏾 👏🏿 🎁 Ultraviolet: effective disinfection and safety 🧑🏿‍🤝‍🧑🏾 🧛🏿 🌩️

The properties of ultraviolet radiation depend on the wavelength, and the ultraviolet of different sources differs in spectrum. We will discuss which sources of ultraviolet radiation and how to apply in order to maximize the bactericidal effect, minimizing the risks of undesirable biological effects.

Fig. 1. The photo does not show UVC disinfection, as you might think, but training in the use of a protective suit with the detection of luminescent spots of training body fluids in UVA rays. UVA is a soft ultraviolet and does not have a bactericidal effect. Closed eyes are a warranted safety measure since the wide range of UVA fluorescent lamps used intersect with UVB, which is hazardous to vision (source Simon Davis / DFID).

The wavelength of visible light corresponds to the energy of a quantum, at which a photochemical action is just becoming possible. Quantums of visible light excite photochemical reactions in a specific photosensitive tissue - in the retina.
Ultraviolet is invisible, its wavelength is shorter, the frequency and energy of the quantum is higher, the radiation is harder, the variety of photochemical reactions and biological effects is greater.

Ultraviolet differs by:

Close in properties to visible light, long-wave / soft / near UVA (400 ... 315 nm);
Medium hardness - UVB (315 ... 280 nm);
Shortwave / far / hard - UVC (280 ... 100 nm).

The bactericidal effect of ultraviolet radiation

Bactericidal action is exerted by hard ultraviolet - UVC, and to a lesser extent ultraviolet of medium hardness - UVB. The bactericidal efficacy curve shows that a clear bactericidal effect has only a narrow range of 230 ... 300 nm, that is, about a quarter of the range called ultraviolet.

Fig. 2 Bactericidal efficiency curves from [ CIE 155: 2003 ]

Quantums with wavelengths in this range are absorbed by nucleic acids, which leads to the destruction of the structure of DNA and RNA. In addition to bactericidal, that is, killing bacteria, this range has a virucidal (antiviral), fungicidal (antifungal) and sporocidal (spore-killing) effects. This includes killing the 2020 pandemic-causing RNA virus SARS-CoV-2.

The bactericidal effect of sunlight

The bactericidal effect of sunlight is relatively small. Let's look at the solar spectrum above the atmosphere and under the atmosphere:

Fig. 3. The spectrum of solar radiation above the atmosphere and at sea level. The toughest part of the ultraviolet range does not reach the earth's surface (borrowed from Wikipedia).

It is worth paying attention to the above-atmospheric spectrum highlighted in yellow. The quantum energy of the left edge of the spectrum of above-atmospheric sunlight with a wavelength of less than 240 nm corresponds to a chemical binding energy of 5.1 eV in the O2 oxygen molecule. Molecular oxygen absorbs these quanta, the chemical bond breaks, atomic oxygen “O” is formed, which combines back into oxygen molecules “O2” and, in part, ozone “O3”.

The solar above-atmospheric UVC forms ozone in the upper atmosphere, called the ozone layer. The chemical bond energy in the ozone molecule is lower than in the oxygen molecule, and therefore ozone absorbs quanta of less energy than oxygen. And if oxygen absorbs only UVC, then the ozone layer absorbs UVC and UVB. It turns out that the sun generates ozone at the very edge of the ultraviolet part of the spectrum, and this ozone then absorbs most of the hard solar ultraviolet radiation, protecting the Earth.

And now, carefully, paying attention to wavelengths and scale, the solar spectrum is compatible with the spectrum of bactericidal action.

Fig. 4 The spectrum of bactericidal action and the spectrum of solar radiation.

It is seen that the bactericidal effect of sunlight is negligible. The part of the spectrum capable of exerting a bactericidal effect is almost completely absorbed by the atmosphere. At different times of the year and in different latitudes, the situation is slightly different, but qualitatively similar.

UV hazard

The head of one of the major countries suggested: "to cure COVID-19, you need to deliver sunlight into the body." However, bactericidal UV destroys RNA and DNA, including human. If you "deliver sunlight into the body" - a person will die.

The epidermis, primarily the stratum corneum of dead cells, protects living tissue from UVC. Below the epidermal layer, only less than 1% of UVC radiation penetrates [WHO]. Longer waves UVB and UVA penetrate to a greater depth.

If there was no solar ultraviolet, perhaps people would not have the epidermis and the stratum corneum, and the surface of the body was mucous, like in snails. But since humans evolved under the sun, only surfaces protected from the sun are mucous. The most vulnerable is the mucous surface of the eye, conditionally protected from solar ultraviolet for centuries, eyelashes, eyebrows, facial motility, and the habit of not looking at the sun.

When they first learned to replace the lens with an artificial one, ophthalmologists were faced with the problem of retinal burns. They began to understand the reasons and found out that the living human lens for ultraviolet radiation is opaque and protects the retina. After that, artificial lenses were made opaque to ultraviolet radiation.

The image of the eye in ultraviolet rays illustrates the opacity of the lens for ultraviolet radiation. It is not worth it to illuminate your own eye with ultraviolet light, as the lens becomes cloudy over time, including due to the dose of ultraviolet radiation accumulated over the years, and needs to be replaced. Therefore, we will take advantage of the experience of brave people who neglected safety, shined a UV flashlight at 365 nm in their eyes, and posted the result on YouTube.

Fig. 5 Frame from the video of the Youtube channel "Kreosan".

365nm luminescent ultraviolet flashlights (UVA) are popular. Bought by adults, but inevitably fall into the hands of children. Children shine these lanterns in their eyes, carefully and for a long time examine the luminous crystal. Such actions are desirable to prevent. If this happens, one can reassure oneself that cataracts in mouse studies are confidently caused by irradiation of the UVB lens, but the cathogenous effect of UVA is unstable [ WHO ].
Nevertheless, the exact spectrum of ultraviolet radiation on the lens is unknown. And if you consider that cataracts are a very delayed effect, you need a certain amount of mind so as not to shine ultraviolet light in your eyes in advance.

The mucous membranes of the eye become inflamed relatively quickly under ultraviolet light, this is called photokeratitis and photoconjunctivitis. The mucous membranes turn red and a sensation of “sand in the eyes” appears. The effect disappears after a few days, but repeated burns can lead to clouding of the cornea.

The wavelengths causing these effects approximately correspond to the weighted UV hazard function given in the standard for photobiological safety [IEC 62471] and approximately coincide with the range of bactericidal action.

Fig. 6 Spectra of UV radiation causing photoconjunctivitis and photokeratitis from [ DIN 5031-10 ] and the weighted function of actinic UV hazard to the skin and eyes from [ IEC 62471 ].

Threshold doses for photokeratitis and photoconjunctivitis 50-100 J / m ² , this value does not exceed the doses used for disinfection. Disinfect the mucous membrane of the eye with ultraviolet light, without causing inflammation, will not work.

Erythema, that is, "sunburn" is dangerous ultraviolet in the range up to 300 nm. According to some sources, the maximum spectral efficiency of erythema at wavelengths of about 300 nm [ WHO ]. The minimum dose that causes barely noticeable erythema of MED (Minimum Erythema Dose) for different skin types ranges from 150 to 2000 J / m² . For residents of the middle band typical MED can be considered a value of about 200 ... 300 J / m ² .

UVB in the range of 280-320 nm, with a maximum of about 300 nm, causes skin cancer. There is no threshold dose, more dose - higher risk, and the effect is delayed.

Fig. 7 Curves of ultraviolet radiation causing erythema and skin cancer.

Photoinduced skin aging is caused by ultraviolet radiation in the entire range of 200 ... 400 nm. There is a well-known photo of a trucker who was exposed to driving ultraviolet radiation at the wheel mainly from the left side. The driver was in the habit of driving with the driver’s window down, but the right side of the face was protected from solar ultraviolet radiation by the windshield. The difference in age of the skin on the right and left side is impressive:

Fig. 8 Photo of a driver who drove a driver’s window [ Nejm ] down for 28 years .

If we roughly estimate that the age of the skin on different sides of this person’s face differs by twenty years, and this is due to the fact that for about the same twenty years, one side of the face was illuminated by the sun and the other not, we can make a cautious conclusion that one day in the open sun day and old skin.

From the reference data [ WHO ] it is known that in the middle latitudes in summer under direct sunshine the minimum erythema dose is 200 J / m ²typed faster than an hour. Comparing these figures with the conclusion made, we can draw another conclusion - skin aging with periodic and short-term work with ultraviolet lamps is not a significant danger.

How much UV is needed for disinfection

The number of surviving microorganisms on surfaces and in the air decreases exponentially with increasing dose of ultraviolet radiation. For example, the dose that kills 90% of mycobacterium tuberculosis is 10 J / m ² . Two such doses kill 99%, three doses kill 99.9%, etc.

Fig. 9 Dependence of the proportion of surviving tuberculosis mycobacteria on the dose of ultraviolet radiation at a wavelength of 254 nm.

The exponential relationship is noteworthy in that even a small dose kills most microorganisms.

Among the pathogenic microorganisms listed in [ CIE 155: 2003 ], Salmonella is the most resistant to ultraviolet radiation. The dose that kills 90% of its bacteria is 80 J / m ² . According to the review [Kowalski2020], the average dose that kills 90% of coronaviruses is 67 J / m ² . But for most microorganisms, this dose does not exceed 50 J / m ² . For practical purposes, you can remember that the standard dose, disinfecting with an efficiency of 90%, is 50 J / m ² .

According to the current procedure for using ultraviolet radiation for air disinfection approved by the Ministry of Health of the Russian Federation [ R 3.5.1904-04 ], the maximum disinfection efficiency of “three nines” or 99.9% is required for operating rooms, maternity hospitals, etc. For school classes, public buildings, etc. enough "one nine", that is, 90% of the destroyed microorganisms. This means that depending on the category of the premises, from one to three standard doses of 50 ... 150 J / m ^{2 are} sufficient .

An example of assessing the required exposure time: for example, it is necessary to disinfect the air and surfaces in a room measuring 5 × 7 × 2.8 meters, for which one Philips TUV 30W open lamp is used.

In the technical description of the lamp, a bactericidal flux of 12 W is indicated [ TUV]. In the ideal case, the entire stream goes strictly to disinfected surfaces, but in a real situation, half of the stream will be lost without benefit, for example, it will excessively intensely illuminate the wall behind the lamp. Therefore, we will count on a useful stream of 6 watts. The total area of the irradiated surfaces in the room - floor 35 m ² + 35 m ceiling ² + walls 67 m ² , a total of 137 m ² .

On average, the flux of bactericidal radiation 6 W / 137 m ² = 0.044 W / m ² falls on the surface . In an hour, that is, in 3600 seconds, a dose of 0.044 W / m ² × 3600 s = 158 J / m ² , or rounded 150 J / m ² , will have to occur on these surfaces. Which corresponds to three standard doses of 50 J / m ² or “three nines” - 99.9% bactericidal efficacy, i.e. operating requirements. And since the calculated dose, before falling to the surface, passed through the volume of the room, the air was also disinfected with no less efficiency.

If the requirements for sterility are small and “one nine” is enough, the considered example requires three times shorter exposure time - rounded up to 20 minutes.

UV protection

The main protective measure during UV disinfection is to leave the room. Being close to a working UV lamp, but looking away will not help, the mucous eyes are irradiated anyway.

A partial measure of protection for the mucous membranes of the eyes may be glass glasses. The categorical statement “glass does not pass ultraviolet” is incorrect, to some extent it does, and different brands of glass are different. But in general, with decreasing wavelength, the transmittance decreases, and UVC is effectively transmitted only by quartz glass. Spectacle glasses in any case are not quartz.

We can confidently say that they do not let in the ultraviolet lenses of glasses marked with UV400.

Fig. 10 Spectrum of transmission of spectacle glasses with indices UV380, UV400 and UV420. Image from the site [ Mitsuichemicals ]

Also a protective measure is the use of sources of the bactericidal range of UVC that do not emit potentially dangerous, but not effective for disinfection, ranges of UVB and UVA.

UV sources

UV diodes

The most common 365 nm UV diodes (UVA) are for “police flashlights,” which cause luminescence to detect contaminants that are invisible without UV light. Disinfection with such diodes is not possible (see Fig. 11).
For disinfection, you can use short-wave UVC diodes with a wavelength of 265 nm. The cost of a diode module that replaces a mercury bactericidal lamp exceeds the cost of the lamp by three orders of magnitude, so in practice such solutions for disinfection of large areas are not used. But there are compact devices on UV diodes for disinfection of small areas - tools, telephones, places of skin damage, etc.

Low pressure mercury lamps

A low-pressure mercury lamp is a standard against which all other sources are compared.
The bulk of the radiation energy of mercury vapor at low pressure in an electric discharge is at a wavelength of 254 nm, which is ideal for disinfection. A small part of the energy is emitted at a wavelength of 185 nm, intensively generating ozone. And a very small amount of energy is emitted at other wavelengths, including the visible range.

In ordinary white-light mercury fluorescent lamps, the glass of the bulb does not transmit ultraviolet radiation emitted by mercury vapor. But the phosphor, a white powder on the walls of the flask, under the influence of ultraviolet light glows in the visible range.

UVB or UVA lamps are arranged in a similar way, the glass bulb does not pass peaks of 185 nm and peak of 254 nm, but the phosphor under the influence of short-wave ultraviolet radiation emits not visible light, but long-wave ultraviolet. These are technical lamps. And since the spectrum of UVA lamps is similar to solar, such lamps are also used for tanning. Comparison of the spectrum with the bactericidal efficiency curve shows that it is not practical to use UVB lamps and especially UVA lamps for disinfection.

Fig. 11 Comparison of the bactericidal efficiency curve, UVB lamp spectrum, UVA tanning lamp spectrum, and 365 nm diode spectrum. Spectra of lamps taken from the site of the American Association of manufacturers of paints [ Paint ].

Note that the spectrum of the UVA fluorescent lamp is wide and captures the UVB range. The spectrum of the 365 nm diode is much narrower, it is “honest UVA”. If UVA is required to induce luminescence for decorative purposes or to detect contamination, using a diode is safer than using an ultraviolet fluorescent lamp.

The UVC low-pressure mercury germicidal lamp differs from the fluorescent ones in that there is no phosphor on the walls of the flask and the bulb passes ultraviolet light. The main line of 254 nm is always skipped, and the ozone-generating line of 185 nm can be left in the spectrum of the lamp or removed by a glass flask with selective transmission.

Fig. 12 The emission range is indicated on the UV marking. The UVC germicidal lamp can be recognized by the absence of a phosphor on the bulb.

Ozone has an additional bactericidal effect, but is a carcinogen, therefore, in order not to wait for the ozone to weather after disinfection, use non-ozone-forming lamps without a 185 nm line in the spectrum. These lamps have an almost perfect spectrum - the main line with a high bactericidal efficiency of 254 nm, very weak radiation in the non-bactericidal ranges of ultraviolet radiation, and a small "signal" radiation in the visible range.

Fig. 13. The spectrum of the UVC low-pressure mercury lamp (provided by lumen2b.ru) is combined with the spectrum of solar radiation (from Wikipedia) and the bactericidal efficiency curve (from the ESNA Lighting Handbook [ ESNA ]).

The blue glow of the bactericidal lamps allows you to see that the mercury lamp is on and working. The glow is faint, and this creates a misleading impression that it is safe to look at the lamp. We do not feel that the radiation in the UVC range is 35 ... 40% of the total power consumed by the lamp.

Fig. 14 A small fraction of the radiation energy of mercury vapor is in the visible range and is visible as a faint blue glow.

A low-pressure bactericidal mercury lamp has the same base as a conventional fluorescent lamp, but a different length is made so that the bactericidal lamp is not inserted into ordinary lamps. The luminaire for a bactericidal lamp, in addition to dimensions, is characterized in that all plastic parts are resistant to ultraviolet radiation, the wires from the ultraviolet are closed, and there is no diffuser.

For home bactericidal needs, the author uses a 15 W bactericidal lamp, previously used to disinfect the nutrient solution of a hydroponic plant. Its analogue can be found on the request "aquarium uv sterilisator". When the lamp is operating, ozone is released, which is not good, but it is useful for disinfecting, for example, shoes.

Fig. 15 Mercury lamps of low pressure with a socle of various types. Images from Aliexpress website.

Medium and high pressure mercury lamps

An increase in mercury vapor pressure complicates the spectrum, the spectrum expands and more lines appear in it, including at ozone-generating wavelengths. The introduction of additives in mercury leads to an even greater complexity of the spectrum. There are many varieties of such lamps, and the spectrum of each is special.

Fig. 16 Examples of spectra of medium and high pressure mercury lamps

An increase in pressure reduces lamp efficiency. Using the Aquafineuv brand as an example, medium-pressure lamps in the UVC area already emit 15-18% of the power consumption, and not 40% as low-pressure lamps. And the cost of equipment per one watt of UVC flux is higher [ Aquafineuv ].
Reduced efficiency and increased cost of the lamp is offset by compactness. For example, disinfection of running water or drying of varnish applied at high speed in printing requires compact and powerful sources, the unit cost and efficiency are unimportant. But to use such a lamp for disinfection is incorrect.

UV irradiator from a DRL burner and a DRT lamp

There is a “popular” way to get a powerful source of ultraviolet light relatively cheaply. Out of use, but still sold DRL lamps white light 125 ... 1000 watts. In these lamps, inside the outer bulb there is a “burner" - a high-pressure mercury lamp. It emits broadband ultraviolet, which is delayed by an external glass bulb, but makes the phosphor on its walls glow. If you break an external flask and connect the burner to the network through a standard choke, you will get a powerful broadband ultraviolet emitter.

Such a makeshift made-up emitter has disadvantages: low efficiency compared to low-pressure lamps, a large proportion of ultraviolet radiation outside the bactericidal range, and you can’t stay in the room for some time after turning off the lamp until ozone decays or disappears.

But the advantages are indisputable: low cost and high power with compact dimensions. The pluses include the generation of ozone. Ozone disinfects shaded surfaces that will not be exposed to ultraviolet rays.

Fig. 17 Ultraviolet irradiator made of DRL lamps. The photo is published with permission of the author, a Bulgarian dentist, using this irradiator in addition to the standard Philips TUV 30W bactericidal lamp.

Similar sources of ultraviolet light for disinfection in the form of high-pressure mercury lamps are used in irradiators of the OUFK-01 "Sun" type.

For example, for the popular lamp "DRT 125-1", the manufacturer does not publish the spectrum, but the documentation gives the parameters: the radiation intensity at a distance of 1 m from the UVA lamp is 0.98 W / m ² , UVB - 0.83 W / m ² , UVC - 0.72 W / m ² , bactericidal flux of 8 W, and after use, room ventilation from ozone is required [ Lisma]. To the direct question about the difference between the DRT lamp and the DRL burner, the manufacturer in his blog replied that the DRT has a warming green coating on the cathodes.

Fig. 18 Source of broadband ultraviolet light - DRT-125 lamp

According to the declared characteristics, it can be seen that the spectrum of broadband with an almost equal share of radiation in soft, medium, and hard ultraviolet, including capturing ozone-generating hard UVC. The bactericidal flow is 6.4% of the power consumption, that is, the efficiency is 6 times less than that of a low-pressure tube lamp.

The manufacturer does not publish the spectrum of this lamp, but the same picture with the spectrum of some of the DRT circulates on the Internet. The original source is unknown, but the ratio of energy in the UVC, UVB and UVA ranges does not correspond to those declared for the DRT-125 lamp. An approximately equal ratio is declared for DRT, and the spectrum shows that the UVB energy is a multiple of the UBC energy. And in UVA it is much higher than in UVB.

Fig. 19. The spectrum of an arc high-pressure mercury lamp, most often illustrating the spectrum of the widely used for medical purposes DRT-125.

It is clear that lamps with different pressures and additives in mercury emit somewhat differently. It is also clear that an uninformed consumer is inclined to imagine the desired characteristics and properties of the product, acquire confidence based on his own assumptions, and make a purchase. And the publication of the spectrum of a specific lamp will cause discussions, comparisons and conclusions.

The author once bought an OUFK-01 installation with a DRT-125 lamp and used it for several years to test the UV resistance of plastic products. He irradiated at the same time two products, one of which was a control of UV-resistant plastic, and looked which yellowed faster. For such an application, knowledge of the exact shape of the spectrum is not necessary, it is only important that the emitter is broadband. But why use broadband ultraviolet if disinfection is required?

The appointment of OUFK-01 indicates that the irradiator is used in acute inflammatory processes. That is, in cases where the positive effect of skin disinfection exceeds the possible harm of broadband ultraviolet radiation. Obviously, in this case, it is better to use narrow-band ultraviolet, without wavelengths in the spectrum that have a different effect except bactericidal.

Air disinfection

Ultraviolet light is considered insufficient to disinfect surfaces, since the rays cannot penetrate where, for example, alcohol penetrates. But ultraviolet disinfects air effectively.

When sneezing and coughing, droplets of several micrometers in size are formed, which hang in the air from several minutes to several hours [ CIE 155: 2003 ]. Studies of tuberculosis have shown that one aerosol drop is sufficient for infection.

On the street, we are in relative safety because of the huge volumes and mobility of air, which can dispel and disinfect anyone and anyone with time and solar radiation. Even in the metro, while the proportion of infected people is small, the total volume of air per one infected person is large, and good ventilation makes the risk of infection spreading small. The most dangerous place during a pandemic of airborne diseases is the elevator. Therefore, sneezers should be quarantined, and air in public areas with insufficient ventilation needs to be disinfected.

Recirculators

One of the options for air disinfection is closed UV recirculators. We will discuss one of such recirculators - “Dezar 7”, known for being seen even in the office of the first person in the state.

The description of the recirculator says that it blows 100 m ³ per hour and is intended for processing a room with a volume of 100 m ³ (approximately 5 × 7 × 2.8 meters).
However, the ability to disinfect 100 m ^{3 of} air per hour does not mean that the air in a room of 100 m ³ per hour will be treated just as efficiently. The treated air dilutes the dirty air, and in this form again and again enters the recirculator. It is easy to build a mathematical model and calculate the effectiveness of such a process:

Fig. 20 Effect of UV recirculator on the number of microorganisms in the air of a room without ventilation.

To reduce the concentration of microorganisms in the air by 90%, the recirculator needs to work more than two hours. In the absence of ventilation in the room, this is possible. But there are no normal rooms with people and without ventilation. For example, [ SP 60.13330.2016 ] prescribes a minimum consumption of outside air during ventilation of 3 m ³ per hour per 1 m ² of apartment area. Which corresponds to a complete air change once an hour and makes the recirculator useless.

If we consider a model not of complete mixing, but of laminar jets that pass along an established complex path in the room and go into ventilation, the benefit of disinfecting one of these jets is even less than in the model of full mixing.

In any case, the UV recirculator is no more useful than an open window.

One of the reasons for the low efficiency of recirculators is that the bactericidal effect in terms of each watt of UV flux is extremely small. The beam passes about 10 centimeters inside the installation, and then it is reflected from aluminum with a coefficient of about k = 0.7. This means that the effective range of the beam inside the installation is about half a meter, after which it is absorbed without benefit.

Fig. 21. A frame from a video on Youtube, on which the recirculator is disassembled. Bactericidal lamps and an aluminum reflective surface are visible, reflecting ultraviolet much worse than visible light [ Dezar ].

A bactericidal lamp that hangs openly on the wall in the office of the clinic and according to the schedule is turned on by the doctor is many times more effective. The rays from an open lamp pass several meters, disinfecting the air first and then also the surfaces.

Top air irradiators

In the wards of hospitals, in which bedridden patients are constantly located, UV installations are sometimes used, which irradiate the circulating air flows under the ceiling. The main drawback of such installations is the lattice that closes the lamps, it allows only rays going in exactly one direction to pass, absorbing without benefit more than 90% of the rest of the stream.

You can additionally blow air through such an irradiator so that at the same time a recirculator is obtained, but this is not done, probably because of the reluctance to get a dust collector in the room.

Fig. 22 Sub-ceiling UV irradiator, image from [ Airsteril ].

Lattices protect people indoors from direct UV radiation, but the stream that passed through the grating hits the ceiling and walls and diffusely reflects, with a reflection coefficient of about 10%. The room is filled with omnidirectional ultraviolet radiation and people receive a dose of ultraviolet radiation proportional to the time spent in the room.

Reviewers and Author

Reviewers:
Artyom Balabanov, electronic engineer, developer of UV curing systems;
Rumen Vasilev, Ph.D., lighting engineer, OOD Interluks, Bulgaria;
Vadim Grigorov, biophysicist;
Stanislav Lermontov, lighting engineer, Integrated Systems LLC;
Alexey Pankrashkin, Ph.D., associate professor, semiconductor lighting and photonics, LLC "INTECH Engineering";
Andrey Khramov, lighting design specialist for medical facilities;
Vitaliy Tsvirko, Head of the Lighting Engineering Testing Laboratory, TSSOT NAS Belarus
Author: Anton Sharakshane, Ph.D., lighting technician and biophysicist, First MGMU named after THEM. Sechenova

References

References

[Airsteril] www.airsteril.com.hk/en/products/UR460
[Aquafineuv] www.aquafineuv.com/uv-lamp-technologies
[CIE 155:2003] CIE 155:2003 ULTRAVIOLET AIR DISINFECTION
[DIN 5031-10] DIN 5031-10 2018 Optical radiation physics and illuminating engineering. Part 10: Photobiologically effective radiation, quantities, symbols and action spectra. . . ,
[ESNA] ESNA Lighting Handbook, 9th Edition. ed. Rea M.S. Illuminating Engineering Society of North America, New York, 2000
[IEC 62471] 62471-2013 .
[Kowalski2020] Wladyslaw J. Kowalski et al., 2020 COVID-19 Coronavirus Ultraviolet Susceptibility, DOI: 10.13140/RG.2.2.22803.22566
[Lisma] lisma.su/en/strategiya-i-razvitie/bactericidal-lamp-drt-ultra.html
[Mitsuichemicals] jp.mitsuichemicals.com/en/release/2014/141027.htm
[Nejm] www.nejm.org/doi/full/10.1056/NEJMicm1104059
[Paint] www.paint.org/coatingstech-magazine/articles/analytical-series-principles-of-accelerated-weathering-evaluations-of-coatings
[TUV] www.assets.signify.com/is/content/PhilipsLighting/fp928039504005-pss-ru_ru
[] . : .
[] youtu.be/u6kAe3bOVVw
[ 3.5.1904-04] 3.5.1904-04
[ 60.13330.2016] 60.13330.2016 , .

UPD: Experimentally released video version of article

Ultraviolet: effective disinfection and safety