Because the Internet is full of more or less reliable sources about the possibilities of fighting viruses, bacteria and other pathogens, it is worth taking a moment to organize knowledge and refute some myths. Especially a lot of legends have accumulated around UV-C lamps and ozonation, so let's take a closer look at them.
UV-C lamps are harmful to health.
Partly true.
UV-C radiation kills microorganisms by damaging their DNA or RNA (more on this in the fight against COVID-19 by UV radiation). If it is harmful, e.g. to bacteria and viruses, then also to animals, plants and people. However, it should be remembered that UV-C radiation only affects those organisms that are exposed to it. So if the light does not shine directly on us, our child or dog, they are completely safe. In short, just turn on the lamp when nobody is in the room and sterilization is 100% safe for us, just like being in the room right after turning off the lamp. It is worth remembering, however, that entering the room immediately after sterilization is safe only in the case of ozone-free lamps. Otherwise, it is necessary to ventilate the room thoroughly!
UV-C radiation penetrates the walls like Wi-Fi.
False.
The UV-C radiation wavelength range is 100 - 280 nm (nanometers), which prevents most obstacles from penetrating. This is the basic reason why bulbs for UV-C lamps cannot be made of ordinary glass but only of special quartz glass. Ordinary glass would not emit radiation outside the interior of the bulb, and that's what sterilization is all about. Such physical properties mean that UV-C light sterilizes the air and the surface that is exposed, but is unable to disinfect behind any obstacle. All you need is a piece of foil, glass or other solid objects to stop UV-C radiation.
Colours fade because of UV light.
True.
UV light actually discolour materials, this is the case with both natural sunlight and UV light artificially produced by the bulbs. That is why it is worth taking care of these objects in advance, which may lose colour depth and not expose them to light, e.g. images. It is worth remembering that photographs in glass frames are safe (glass stops UV radiation).
UV-C light is the same as solar light and helps plants in photosynthesis.
False.
The sun emits UV-C radiation, but fortunately for us it does not reach the surface of our planet because it is retained in the upper atmosphere. UV-C is radiation harmful to all living organisms, including plants. What kills bacteria and viruses also damages larger organisms, e.g. plants. Therefore, long exposure of plants with UV-C lamps will lead to their dying.
UV-C radiation kills bacteria, mites and fungi, but not viruses.
False.
To understand why this sentence is false, it's best to read the text: Can you fight COVID-19 using UV light?. In short, UV-C radiation destroys DNA and RNA chains and as a result pathogens die or permanently lose their ability to reproduce. DNA or RNA is found in bacteria, mites, fungi and viruses, so UV-C acts on every pathogen listed, including viruses.
UV-C irradiated objects are carcinogenic.
Partly true.
UV-C radiation (wavelength 100 nm - 380 nm) is not the same as X-rays (wavelength 10 pm [picometers] - 10 nm). The UV-C wave does not penetrate walls or even ordinary cardboard or plastic. If it is not able to penetrate the paper, it can not be irradiated with anything behind an obstacle. To do justice, however, it should be noted that UV-C is invisible and has a great impact on skin aging and can initiate cancer as well as sunlight. To avoid the risk, just leave the room where the UV-C lamp is turned on. UV-C irradiated space and products do not become carcinogenic.
You cannot expose food to UV-C light.
Partly true.
We must first divide food into two categories: packaged products, and vegetables, meat, and fruits. There are no contraindications to irradiating all kinds of food packaging for sterilization. So if you think that any package of yogurt, juice, flour, etc. should be disinfected after bringing them from the store, you can use UV-C light without any problems. It is important not to do it with products without packaging, which can spoil them much faster than suggested on the due to date. Therefore, do not expose fruit, vegetables, meat, juice or e.g. milk directly. However, if you want to disinfect e.g. previously washed dishes, feel free to do so.
UV-C light does not pass through glass or plastic.
True.
The wavelength of UV-C light does not allow it to pass through ordinary glass or plastic. It is for this reason that UV-C radiators (bulbs) are made of special quartz glass, which allows easy penetration of UV-C radiation. However, quartz glass is not widely used and there are no obstacles to observing the operation of UV-C lamps from behind a standard glass. Similar is the case with Plexiglas, which stops UV-C radiation. Currently, manufacturers are looking for special transparent materials that allow UV-C light to pass, so far only quartz glass and special silicones are commonly used.