The properties of ultraviolet depend on the wavelength, and the ultraviolet of different sources differs in spectrum. Let's discuss which UV sources and how to use them to maximize bactericidal action while minimizing the risks of undesirable biological effects.
Rice. 1. The photo does not show disinfection with UVC radiation, as you might think, but a training in the use of a protective suit with the detection of luminescent spots of training bodily fluids in UVA rays. UVA is a soft ultraviolet and does not have a bactericidal effect. Keeping your eyes closed is a reasonable safety measure, as the wide spectrum UVA fluorescent lamp you use interferes with UVB, which is harmful to your eyes (Source: Simon Davis/DFID).
The wavelength of visible light corresponds to the quantum energy at which photochemical action is only just becoming possible. Visible light quanta 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 are higher, the radiation is harder, the variety of photochemical reactions and biological effects is greater.
Ultraviolet is divided into:
- Similar 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
The bactericidal effect is exerted by hard ultraviolet - UVC, and to a lesser extent ultraviolet of medium hardness - UVB. According to the curve of bactericidal efficiency, it can be seen that only a narrow range of 230–300 nm, that is, about a quarter of the range called ultraviolet, has a clear bactericidal effect.
Rice. 2 Curves of bactericidal efficacy from []
Quanta 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 virucidal (antiviral), fungicidal (antifungal) and sporicidal (spore-killing) effects. Including the RNA-containing virus SARS-CoV-2020 that caused the 2 pandemic is being killed.
The bactericidal effect of sunlight
The bactericidal effect of sunlight is relatively small. Let's look at the solar spectrum above and below the atmosphere:
Rice. 3. The spectrum of solar radiation above the atmosphere and at sea level. The hardest 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 supraatmospheric solar rays with a wavelength of less than 240 nm corresponds to the chemical bond energy of 5.1 eV in the oxygen molecule "O2". Molecular oxygen absorbs these quanta, the chemical bond breaks, atomic oxygen "O" is formed, which combines back into oxygen molecules "O2" and, partially, ozone "O3".
Solar supraatmospheric UVC produces ozone in the upper atmosphere, called the ozone layer. The energy of the chemical bond 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 at the very end of the ultraviolet part of the spectrum generates ozone, and this ozone then absorbs most of the hard solar ultraviolet, protecting the Earth.
And now, carefully, paying attention to wavelengths and scale, let's combine the solar spectrum with the spectrum of bactericidal action.
Rice. 4 Spectrum of bactericidal action and spectrum of solar radiation.
It can be seen that the bactericidal effect of sunlight is insignificant. 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 at different latitudes, the situation is slightly different, but qualitatively similar.
The danger of ultraviolet
The head of one of the major countries suggested: “to cure COVID-19, you need to deliver sunlight into the body.” However, germicidal UV destroys RNA and DNA, including human ones. If "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 UVB and UVA wavelengths penetrate deeper.
If there was no solar ultraviolet, perhaps people would not have an epidermis and a stratum corneum, and the surface of the body would be mucous, like in snails. But since humans evolved under the sun, only sun-sheltered surfaces are slimy. The most vulnerable is the mucous surface of the eye, conditionally protected from solar ultraviolet radiation by eyelids, eyelashes, eyebrows, facial motility, and the habit of not looking at the sun.
When they first learned how to replace the lens with an artificial one, ophthalmologists faced the problem of retinal burns. They began to understand the reasons and found out that a living human lens for ultraviolet radiation is opaque and protects the retina. After that, they began to make artificial lenses opaque to ultraviolet.
The image of the eye in ultraviolet rays illustrates the opacity of the lens to ultraviolet light. You should not illuminate your own eye with ultraviolet light, because over time the lens becomes cloudy, including due to the dose of ultraviolet light accumulated over the years, and needs to be replaced. Therefore, we will use the experience of brave people who neglected safety, shone their eyes with an ultraviolet flashlight at a wavelength of 365 nm, and posted the result on YouTube.
Rice. 5 A frame from the Kreosan Youtube channel video.
Luminescence-inducing 365 nm ultraviolet (UVA) flashlights are popular. Bought by adults, but inevitably fall into the hands of children. Children shine these flashlights into their eyes, carefully and for a long time examine the luminous crystal. It is desirable to prevent such actions. If this is the case, one can reassure oneself that cataracts in mouse studies are confidently caused by UVB lens irradiation, but the catarrhogenic effect of UVA is unstable [].
And yet the exact spectrum of action of ultraviolet radiation on the lens is unknown. And given that cataracts are a highly delayed effect, it takes a certain amount of intelligence not to shine ultraviolet light into 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 become red, and there is a feeling of "sand in the eyes." The effect wears off after a few days, but repeated burns can lead to clouding of the cornea.
The wavelengths causing these effects roughly correspond to the weighted UV hazard function given in the photobiological safety standard [IEC 62471] and are roughly the same as the germicidal range.
Rice. 6 Action spectra of ultraviolet light causing photoconjunctivitis and photokeratitis from [] and the weighted function of the actinic UV skin and eye hazard from [].
Threshold doses for photokeratitis and photoconjunctivitis are 50-100 J/m2, this value does not exceed the doses used for disinfection. It will not work to disinfect the mucous membrane of the eye with ultraviolet light without causing inflammation.
Erythema, that is, "sunburn" is dangerous ultraviolet in the range up to 300 nm. According to some sources, the maximum spectral efficiency of erythema is at wavelengths of about 300 nm []. The minimum dose that causes barely noticeable erythema MED (Minimum Erythema Dose) for different skin types ranges from 150 to 2000 J/m2. For residents of the middle lane, a typical EDR value can be considered to be about 200…300 J/m2.
UVB in the range of 280-320 nm, with a maximum around 300 nm, causes skin cancer. There is no threshold dose, more dose - higher risk, and the effect is delayed.
Rice. 7 UV action curves causing erythema and skin cancer.
Photoinduced skin aging is caused by ultraviolet light in the entire range of 200–400 nm. There is a photograph of a trucker who was exposed to solar ultraviolet radiation while driving, mainly from the left side. The driver had a habit of driving with the driver's window down, but the right side of his face was protected from the sun's ultraviolet by the windshield. The difference in the age condition of the skin on the right and left sides is impressive:
Rice. 8 Photograph of a driver who drove with the driver's window rolled down for 28 years [].
If we roughly estimate that the age of the skin on different sides of the face of this person differs by twenty years, and this is a consequence of the fact that for about the same twenty years one side of the face was illuminated by the sun, and the other was not, we can cautiously conclude that a day under the open sun is one day and ages the skin.
From reference data [] it is known that in mid-latitudes in summer under direct sun, the minimum erythemal dose of 200 J/m2 is accumulated in less than an hour. Comparing these figures with the conclusion made, one more conclusion can be drawn - skin aging during periodic and short work with ultraviolet lamps is not a significant danger.
How much ultraviolet light is needed for disinfection
The number of surviving microorganisms on surfaces and in the air decreases exponentially with an increase in the dose of ultraviolet radiation. For example, the dose that kills 90% of Mycobacterium tuberculosis is 10 J/m2. Two such doses kill 99%, three doses kill 99,9%, and so on.
Rice. 9 Dependence of the proportion of surviving Mycobacterium tuberculosis on the dose of ultraviolet radiation at a wavelength of 254 nm.
The exponential dependence is remarkable in that even a small dose kills most of the microorganisms.
Among those listed in [] pathogenic microorganisms most resistant to ultraviolet salmonella. The dose that kills 90% of its bacteria is 80 J/m2. According to the review [Kowalski2020], the average dose that kills 90% of coronaviruses is 67 J/m2. But for the majority of microorganisms, this dose does not exceed 50 J/m2. For practical purposes, it can be remembered that the standard dose that disinfects with 90% efficiency is 50 J/m2.
According to the current methodology approved by the Ministry of Health of Russia for the use of ultraviolet radiation for air disinfection [] maximum disinfection efficiency of "three nines" or 99,9% is required for operating rooms, maternity hospitals, etc. For school classes, public buildings, etc. “one nine” is sufficient, that is, 90% of the destroyed microorganisms. This means that, depending on the category of the room, one to three standard doses of 50 ... 150 J / m2 are sufficient.
Example of estimating the required exposure time: Let's say you need to disinfect the air and surfaces in a room measuring 5 × 7 × 2,8 meters, for which one open Philips TUV 30W lamp is used.
The technical description of the lamp indicates a germicidal flux of 12 W []. In the ideal case, the entire flow goes strictly to the disinfected surfaces, but in a real situation, half of the flow will be wasted, for example, it will illuminate the wall behind the lamp excessively intensively. Therefore, we will rely on a useful flow of 6 watts. The total irradiated surface area in the room is 35 m2 floor + 35 m2 ceiling + 67 m2 walls, total 137 m2.
On average, the flux of bactericidal radiation falls on the surface 6 W/137m2 = 0,044 W/m2. In an hour, that is, in 3600 seconds, these surfaces will receive a dose of 0,044 W/m2 × 3600 s = 158 J/m2, or rounded 150 J/m2. Which corresponds to three standard doses of 50 J / m2 or “three nines” - 99,9% bactericidal effectiveness, i.e. operating room requirements. And since the calculated dose, before falling on the surface, passed through the volume of the room, the air is disinfected with no less efficiency.
If the requirements for sterility are small and “one nine” is enough, for the considered example, a three times shorter exposure time is needed - rounded 20 minutes.
Protection from ultraviolet radiation
The main protective measure during UV disinfection is to leave the premises. Being close to a working UV lamp, but looking away will not help, the mucous eyes are still irradiated.
Glass glasses can be a partial measure of protection of the mucous membranes of the eye. The categorical statement “glass does not transmit ultraviolet” is incorrect, it does pass to some extent, and different brands of glass are different. But in general, as the wavelength decreases, the transmittance decreases, and UVC is effectively transmitted only by quartz glass. Spectacle glasses are not quartz in any case.
We can confidently say that the lenses of glasses marked UV400 do not let through ultraviolet.
Rice. 10 Transmission spectrum of spectacle glasses with indices UV380, UV400 and UV420. Image from the site []
It is also a protective measure to use sources of the bactericidal UVC range that do not emit potentially dangerous, but not effective for disinfection, UVB and UVA ranges.
UV Sources
UV diodes
The most common 365 nm ultraviolet (UVA) diodes are designed for "police flashlights" that cause luminescence to detect contaminants invisible without UV light. Disinfection with such diodes is not possible (see Fig. 11).
For disinfection, short-wavelength UVC diodes with a wavelength of 265 nm can be used. The cost of a diode module that would replace a mercury germicidal lamp is three orders of magnitude higher than the cost of a lamp, so in practice such solutions are not used for disinfection of large areas. But there are compact devices based on UV diodes for disinfection of small areas - tools, telephones, skin lesions, etc.
Low pressure mercury lamps
The low pressure mercury lamp is the standard by which all other sources are compared.
The main part of the radiation energy of mercury vapor at low pressure in an electric discharge falls on a wavelength of 254 nm, which is ideal for disinfection. A small part of the energy is emitted at a wavelength of 185 nm, which generates intense ozone. And a very small amount of energy is emitted at other wavelengths, including the visible range.
In conventional white light mercury fluorescent lamps, the bulb glass does not transmit ultraviolet radiation emitted by mercury vapor. But the phosphor, a white powder on the walls of the flask, glows in the visible range under the action of ultraviolet radiation.
UVB or UVA lamps are arranged in a similar way, the glass bulb does not transmit peaks of 185 nm and a peak of 254 nm, but the phosphor under the action of short-wave ultraviolet does not emit visible light, but long-wave ultraviolet. These are industrial lamps. And since the spectrum of UVA lamps is similar to the sun, such lamps are also used for tanning. Comparison of the spectrum with the curve of bactericidal efficiency shows that it is not advisable to use UVB lamps and even more so UVA for disinfection.
Rice. 11 Comparison of germicidal efficacy curve, UVB lamp spectrum, UVA tanning lamp spectrum and 365nm diode spectrum. The spectra of the lamps are taken from the website of the American Paint Manufacturers Association [].
Note that the spectrum of a UVA fluorescent lamp is wide and covers the UVB range. The spectrum of the 365 nm diode is much narrower, this 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.
A low-pressure UVC mercury bactericidal lamp differs from fluorescent ones in that there is no phosphor on the walls of the bulb, and the bulb transmits ultraviolet light. The main 254 nm line is always passed through, while the 185 nm ozone generating line can be left in the lamp spectrum or removed with a selective transmission glass bulb.
Rice. 12 The radiation range is indicated on the marking of UV lamps. A germicidal UVC 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 ozone to weather after disinfection, non-ozone-forming lamps without a 185 nm line in the spectrum are used. These lamps have an almost perfect spectrum - a main line with a high germicidal efficiency of 254 nm, very weak radiation in the non-germicidal ultraviolet ranges, and a small "signal" radiation in the visible range.
Rice. 13. The spectrum of a low-pressure UVC mercury lamp (provided by the journal lumen2b.ru) is combined with the spectrum of solar radiation (from Wikipedia) and the bactericidal efficacy curve (from ESNA Lighting Handbook []).
The blue glow of germicidal lamps allows you to see that the mercury lamp is on and working. The glow is weak, and this creates a deceptive impression that it is safe to look at the lamp. We do not feel that the UVC radiation is 35-40% of the total power consumed by the lamp.
Rice. 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 germicidal mercury lamp has the same base as a conventional fluorescent lamp, but is made of a different length so that the germicidal lamp is not inserted into ordinary lamps. The luminaire for a germicidal lamp, in addition to dimensions, is distinguished by the fact that all plastic parts are UV-resistant, the UV wires are closed, and there is no diffuser.
For home germicidal needs, the author uses a 15 W germicidal lamp, previously used to decontaminate the nutrient solution of a hydroponic setup. Its analogue can be found at the request "aquarium uv sterilisator". When the lamp is on, ozone is released, which is not good, but it is useful for disinfecting, for example, shoes.
Rice. 15 Low pressure mercury lamps with bases of various types. Images from the Aliexpress website.
Medium and high pressure mercury lamps
An increase in mercury vapor pressure leads to a complication of the spectrum, the spectrum expands and more lines appear in it, including those at ozone-generating wavelengths. The introduction of additives into mercury leads to an even greater complication of the spectrum. There are many varieties of such lamps, and the spectrum of each is special.
Rice. 16 Examples of spectra of medium and high pressure mercury lamps
Increasing the pressure reduces the efficiency of the lamp. Using the example of the Aquafineuv brand, medium pressure lamps in the UVC area already emit 15-18% of the power consumed, and not 40% as low pressure lamps. And the cost of equipment per watt of UVC flow is higher [].
The decrease in efficiency and increase in the cost of the lamp is offset by compactness. For example, the disinfection of running water or the drying of varnish applied at high speed in the printing industry require compact and powerful sources, unit cost and efficiency are not important. But using such a lamp for disinfection is incorrect.
UV irradiator from a DRL burner and a DRT lamp
There is a "folk" way to get a powerful source of ultraviolet relatively inexpensively. They are going out of use, but 125 ... 1000 W white light DRL lamps are still sold. In these lamps, inside the outer flask there is a “burner” - a high-pressure mercury lamp. It emits broadband ultraviolet, which is delayed by the outer glass bulb, but causes the phosphor on its walls to glow. If you break the outer flask and connect the burner to the network through a standard throttle, you get a powerful emitter of broadband ultraviolet radiation.
Such a handicraft 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 the lamp is turned off until the ozone decays or disappears.
But the advantages are undeniable: low cost and high power with compact dimensions. Ozone generation is also a plus. Ozone disinfects shaded surfaces that are not exposed to ultraviolet rays.
Rice. 17 An ultraviolet irradiator made from DRL lamps. The photo is published with the permission of the author, a Bulgarian dentist using this illuminator in addition to a standard Philips TUV 30W germicidal lamp.
Similar sources of ultraviolet for disinfection in the form of high-pressure mercury lamps are used in irradiators of the OUFK-01 "Solnyshko" type.
For example, for the popular DRT 125-1 lamp, the manufacturer does not publish the spectrum, but the documentation provides the following parameters: irradiation intensity at a distance of 1 m from the lamp UVA - 0,98 W / m2, UVB - 0,83 W / m2, UVC – 0,72 W/m2, bactericidal flux 8 W, and after use ventilation of the room from ozone is required []. To a direct question about the difference between a DRT lamp and a DRL burner, the manufacturer answered in his blog that the DRT has an insulating green coating on the cathodes.
Rice. 18 Source of broadband ultraviolet - lamp DRT-125
According to the declared characteristics, it can be seen that the spectrum is broadband with an almost equal share of radiation in the soft, medium, and hard ultraviolet, including the hard UVC that generates ozone. The germicidal flux is 6,4% of the power input, that is, the efficiency is 6 times less than that of a low pressure tubular lamp.
The manufacturer does not publish the spectrum of this lamp, and the same picture with the spectrum of some 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. For DRT, an approximately equal ratio is declared, and the spectrum shows that the UVB energy is a multiple of the UBC energy. And UVA is much higher than UVB.
Rice. 19. Spectrum of a high-pressure mercury arc lamp, which most often illustrates the spectrum of DRT-125 widely used for medical purposes.
It is clear that lamps with different pressures and mercury additions emit somewhat differently. It is also understood that the uninformed consumer tends to independently imagine the desired characteristics and properties of the product, acquire confidence based on their own assumptions, and make a purchase. And the publication of the spectrum of a particular lamp will cause discussions, comparisons and conclusions.
The author once bought an OUFK-01 unit with a DRT-125 lamp and used it for several years to test the UV resistance of plastic products. I irradiated two products at the same time, one of which was a control made of UV-resistant plastic, and watched which one would turn yellow faster. For such an application, knowledge of the exact shape of the spectrum is not necessary, it is only important that the emitter be broadband. But why use broadband ultraviolet if disinfection is required?
In the appointment of OUFK-01, it is indicated 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 an effect other than bactericidal.
Air disinfection
Ultraviolet is recognized as an insufficient means for disinfecting surfaces, since the rays cannot penetrate where, for example, alcohol penetrates. But ultraviolet light effectively disinfects the air.
When sneezing and coughing, droplets a few micrometers in size are formed, which hang in the air from several minutes to several hours []. Tuberculosis studies have shown that a single aerosol drop is sufficient for infection.
On the street, we are relatively safe because of the huge volumes and mobility of air that can dispel and disinfect any sneeze with time and solar radiation. Even in the subway, as long as the proportion of infected people is small, the total air volume per infected person is high, and good ventilation makes the risk of spreading the infection small. The most dangerous place during pandemics of airborne diseases is the elevator. Therefore, sneezers should be quarantined, and the air in public spaces with insufficient ventilation needs to be disinfected.
Recirculators
One of the options for air disinfection is closed UV recyclers. Let's discuss one of these recirculators - Dezar 7, known for being seen even in the office of the first person of the state.
The description of the recirculator says that it blows 100 m3 per hour and is designed to treat a room with a volume of 100 m3 (approximately 5 × 7 × 2,8 meters).
However, the ability to disinfect 100 m3 of air per hour does not mean that the air in a 100 m3 per hour room will be treated as effectively. 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:
Rice. 20 Influence of UV recirculator operation 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 for more than two hours. In the absence of ventilation in the room, this is possible. But there are no rooms with people and without ventilation in the norm. Eg, [] prescribes a minimum outdoor air flow rate for ventilation of 3 m3 per hour per 1 m2 of the area of the apartment. Which corresponds to a complete replacement of air once an hour and makes the work of the recirculator useless.
If we consider a model not of full mixing, but of laminar jets that pass along an established complex trajectory in the room and go into ventilation, the benefit of disinfecting one of these jets is even less than in the full mixing model.
In any case, a 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 is extremely small in terms of each watt of UV flux. The beam passes about 10 centimeters inside the installation, and then is reflected from aluminum with a coefficient of about k=0,7. This means that the effective path of the beam inside the installation is about half a meter, after which it is absorbed uselessly.
Rice. 21. A frame from a Youtube video showing the disassembly of the recycler. Germicidal lamps and an aluminum reflective surface are visible, reflecting ultraviolet much worse than visible light [].
A bactericidal lamp, which is openly hanging on the wall in the clinic's office and turned on by the doctor according to the schedule, is many times more effective. The rays from an open lamp travel several meters, first disinfecting the air, and then also the surfaces.
Air ventilators in the upper part of the room
In hospital wards, in which bedridden patients are constantly located, UV installations are sometimes used that irradiate circulating air flows under the ceiling. The main disadvantage of such installations is that the grating that covers the lamps allows only beams that go strictly in one direction to pass, absorbing more than 90% of the rest of the flow without benefit.
You can additionally blow air through such an irradiator to make a recirculator at the same time, but this is not done, probably because of the reluctance to get a dust collector in the ward.
Rice. 22 Under-ceiling UV air irradiator, image from the site [].
The gratings protect people in the room from a direct stream of ultraviolet radiation, but the stream that passed through the grating hits the ceiling and walls and is diffusely reflected, with a reflectance 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, electronics engineer, developer of UV curing systems;
Rumen Vasilev, Ph.D., lighting engineer, Interlux OOD, Bulgaria;
Vadim Grigorov, biophysicist;
Stanislav Lermontov, lighting engineer, Integrated Systems LLC;
Aleksey Pankrashkin, Ph.D., Associate Professor, Semiconductor Lighting Engineering and Photonics, INTECH Engineering LLC;
Andrey Khramov, lighting design specialist for medical institutions;
Vitaly Tsvirko, Head of the Lighting Testing Laboratory of the TsSOT NAS of Belarus
Author: Anton Sharakshane, Candidate of Physical and Mathematical Sciences, lighting engineer and biophysicist, First Moscow State Medical University. THEM. Sechenov
references
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[Aquafineuv]
[CIE 155:2003] CIE 155:2003 ULTRAVIOLET AIR DISINFECTION
[DIN 5031-10] DIN 5031-10 2018 Optical radiation physics and illuminating engineering. Part 10 Physics of optical radiation and lighting engineering. Photobiologically active radiation. Sizes, symbols and action spectra
[ESNA] ESNA Lighting Handbook, 9th Edition. ed. Rea MS Illuminating Engineering Society of North America, New York, 2000
[IEC 62471] GOST R IEC 62471-2013 Lamps and lamp systems. Light biological safety
[Kowalski2020] Wladyslaw J. Kowalski et al., 2020 COVID-19 Coronavirus Ultraviolet Susceptibility, DOI: 10.13140/RG.2.2.22803.22566
[Lisma]
[Mitsui chemicals]
[Name]
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[WHO] World Health Organization. Ultraviolet Radiation: The official scientific overview of the effects of UV radiation on the environment and health, with reference to global ozone depletion.
[Dezar]
[R 3.5.1904-04] R 3.5.1904-04 Use of ultraviolet germicidal radiation for indoor air disinfection
[SP 60.13330.2016] SP 60.13330.2016 Heating, ventilation and air conditioning.
Source: habr.com