With the health crisis, more and more manufacturers are offering UV solutions to sterilize your electronic devices and objects of all kinds. But how does this technology work and is it reliable? This is what we will see in this dossier thanks, in particular, to the enlightened explanations of two CNRS researchers.
In recent months, we have seen more and more cases for smartphones promising wonders to who will use them. The idea behind these boxes, with very classic appearances, is to “Clean”, “Sterilize”, “Eliminate” bacteria from your everyday objects, whether they are glasses or a smartphone.
To do this, the manufacturers indicate that they have installed UV lamp systems inside the box. Sometimes even the integration of these UV lights is part of the functions offered by a product. This is the case, for example, on LG’s Tone Free FN6 headphones, which will be tested very soon on Frandroid.
But how do these sterilization boxes work and are they really effective? This is what we will be looking at in this article.
UV-C rays that will attack bacteria
First of all, it should be explained that manufacturers almost never communicate on the elimination of all bacteria. Generally, brands indicate that their devices allow sterilization that will remove 99 or 99.9% of bacteria. It is also generally on the most common bacteria that manufacturers communicate, whether it is E.coli or S. aureus in the case of LG for example. If viruses can also be destroyed, it is more complicated. Most manufacturers do not dare to communicate on a destruction of Sars-Cov-2, at the origin of Covid-19 for example.
To understand the operation of these ultraviolet boxes, it is also necessary to understand the nature of ultraviolet (UV) radiation. These are electromagnetic waves with a length of between 100 and 400 nm, just below visible light. There are actually three types of ultraviolet waves: UV-A (315 to 400 nm), UV-B (280 to 315 nm) and UV-C (100 to 280 nm). In the case of sterilization, it is particularly UV-C, those furthest from visible light, that will interest us. It must be said that this is the most dangerous ultraviolet radiation for living things, since they have a shorter wavelength. “UV-C are more energetic so they do more damage to the DNA of viruses and this is what will make it possible to inactivate the virus”, explains Géraldine Dantelle, researcher at the CNRS.
However, in a natural environment, UV-C is largely filtered by the atmosphere and has no effect on the body. In a sterilization box, on the other hand, we will rely on this dangerousness to attack living matter, and therefore bacteria. The idea is then to emit UV-C to attack the DNA of germs and make them inoperative.
Systems already used in laboratories
These sterilization systems have been known and used for decades to remove bacteria, whether to sterilize laboratory equipment or to remove bacteria in running water for almost a century. Nevertheless, luminous devices were hitherto massive, intended for professional use and came in the form of mercury pressure lamps. With small cases barely larger than a smartphone, or earphone cases, one could doubt a similar efficiency.
Nevertheless, at LG or at Samsung, we communicate on sterilization in just ten minutes, with studies carried out in the laboratory to support these statements, whether it is the TÜV SÜD organization in the case of the first or the SGS-CSTC firm for the second. In medical research laboratories, sterilization can take about 30 minutes. Nevertheless, according to Mireille Ansaldi, research director at CNRS, “The infectious load on headphones or a smartphone is not going to be huge, so 10 minutes is enough on this type of device. On headphones or glasses, there are not necessarily pathogens ”.
These boxes are also generally equipped with several UV LEDs in order to promote the reflection of UV-C rays. Concretely, when you close the case and activate the cleaning mode, the case will automatically emit UV-C rays. Some, like the Samsung model, will even allow accessory functions such as wireless charging at the same time. Once the case is opened, the radiation stops. However, it may display a blue light. Don’t panic, this is purely decorative light and not ultraviolet radiation which is, by definition, invisible to the naked eye. “In order to emit UV-C radiation, lamps or LEDs must be fitted with a specific filter. They are also high power lamps. To have effects, you need sufficient energy, measured in joule / cm² ”, tells us Mireille Ansaldi.
Essential characteristics for the operation of the boxes
However, where most manufacturers go wrong in their communication on UV units, it is on the characteristics side. Many of them announce a 99 or 99.9% elimination of bacteria, results – not public – from supporting laboratories. Nevertheless, few are the manufacturers to give all the characteristics of these UV lamps.
On the side of Belkin, Samsung or LG for example, impossible to know the emission power of these lamps, nor their lifespan or the emitted wavelength. However, these characteristics are essential to ensure effective sterilization.
For the wavelength for example, UV-C may be between 100 and 280 nm, all values are not equal to attack bacteria. “The wavelength which allows the best sterilization is between 230 nm and 260 with a peak at 260 nm: it is the most efficient wavelength”, Mireille Ansaldi tells us. However, based on a technical sheet or on the manufacturers’ website, it is impossible to verify this data. LG, which was the only manufacturer to answer us, nevertheless gave us the wavelength emitted on the sterilization unit of its headphones, at 275 nm.
It is therefore UV-C, but they are similar to UV-B. However, this could pose some efficiency problems, as Geraldine Dantelle tells us: “ The more we go towards UV-B and A, the lower the energy of the radiation, so the lower the energy load will be ”. Currently, research is also moving towards UV-C solutions going below the 254 nm offered by current solutions: “LEDs below 250 nm are not yet commercial. It is a research direction to offer LEDs with a deeper UV-C length. The deeper UV-C, below 250 nm, would be less dangerous for humans, because they would be blocked by dead skin cells ”.
The power emitted per cm²
For the power emitted, measured in J / m², there too is radio silence on the manufacturers’ websites. However, the more powerfully the ultraviolet rays emitted, the more effective the sterilization will be. You can’t light an entire stadium with a single lighter.
The power of UV-C rays to destroy bacteria will therefore depend on the bacteria in question. For E. Coli, exposure to a dose of 27 mJ / cm² thus allows 99.999% of the organisms. Overall, a dose of less than 100 mJ / cm² is thus sufficient to destroy the overwhelming majority of bacteria. It still remains to know the dose emitted by the ampoules of the devices. For LG, which was the only one to answer our questions, the UVNano housing of its headphones emits a dose of 300 mJ / cm². Suffice to say that it is largely sufficient for effective sterilization.
In addition, an important factor will be the size of the case, and therefore the proximity between the LEDs emitting UV-C and bacteria, as Geraldine Dantelle tells us: “The dose depends on the distance between the product and the lamp to maintain the intensity. The boxes being small, with a nearby lamp, the dose is not negligible. The closer the lamp, the more effective the sterilization ”.
The life of the bulb is also important, even if it is an LED, more enduring than a conventional battery. “On UV sterilization equipment in the laboratory, the lamp must be changed regularly to maintain correct efficiency and power. The power decreases as the service life increases. The lifespan is a few hundred hours for a UV lamp ”, explains Mireille Ansaldi.
On a consumer sterilization box equipped with LEDs, this lifespan is not unlimited either, but it is much longer.“Conventional UV-C lamps are mercury pressure lamps that have a limited lifespan. The advantage of LEDs is their much longer lifespan, which can be counted in tens of thousands of hours ”, indicates for its part Geraldine Dantelle. At LG, we specify that the UVNano housing of its headphones incorporates LEDs with a lifespan of 43,700 hours.
A need for more transparency on the part of manufacturers
As we have seen, the most useful data for verifying the effectiveness of a UV sterilization product are therefore the emitted dose, the wavelength or the lifespan of the LEDs. However, if the manufacturers generally communicate on a percentage of destroyed bacteria, or on rarely published laboratory results, they are very little to communicate on the precise characteristics of these devices.
However, like the capacity of a smartphone battery or the GPU integrated in a laptop PC, this is an essential characteristic of these sterilization boxes. It is in the light of these data that consumers will be able to know whether a case will prove useful or if it is just a simple gadget, just good for preventing a phone from taking dust in the air. ‘outside.
If manufacturers want to take this new market seriously, they will therefore have to communicate real data.