New LED-Enabled Disinfection Concept Against Corona Fall Back
UV Disinfection Principles
Although invisible to the human eye, UV light is widely used in many industrial segments due to its highly reactive nature. Its reactive property comes from the fact that photons in the UV range oscillate at very high frequencies, carrying a lot of energy ( E=hν, where Plank’s constant; ν = frequency of the photon). When UV photons collide with the electrons of an atom (e.g., oxygen), they bring the atom into an excited state, making it much more reactive. When UV photons hit the DNA molecule, they inactivate it by introducing defects into its structure. UV photons can also create free radicals that can damage the DNA molecule even further, along with some other critical molecules within the cell, causing it to die. With some intelligent engineering, this property of the UV light can be leveraged to fight many kinds of pathogens, including dangerous viruses such as the novel SARS COV-2 (COVID-19) virus, in many different applications, where other methods of disinfection are not appropriate or best-suited.
General on Disinfection
Disinfection never kills all microbes. It is a statistical process where the amount of pathogens gets significantly reduced. Typically, removal of 99.9% or 99.99% of pathogens is sufficient for many applications. Also, 90% pathogen reduction (approximately the percentage of protection provided by protective face masks) can be beneficial, as well. For example, boiling water will not remove 100% of the pathogens, especially when considering the whole process, where re-contamination from surviving microbes and carry-overs can become significant. Also, in the process of disinfection, not only pathogens and viruses are removed, but also a useful microbiome, which creates the right conditions for various other pathogens to repopulate. Therefore, after the initial irradiation (e.g., against viruses), the procedure should be repeated for thorough disinfection against the repopulating bacteria and fungi.
The wavelength of UV light ranges between 100 nm to 430 nm and is divided into three bands: UV-C (100 to 280 nm), UV-B (280 to 315 nm), and UV-A (315 to 380 nm). Different UV bands carry different amounts of energy and have different effects on DNA molecules and cells, in general. On the other hand, living organisms have developed defense mechanisms during their evolution, as the sun is a natural source of UV radiation. Typically, many bacteria and viruses have low to medium resistance against blue and UV light – commonly used reference pathogen is E. Coli. Conversely, fungi and its spores are significantly more challenging to disinfect with the UV light, due to their naturally developed defense mechanisms (A. Niger is a prominent template for such microbes).
Disinfection with the UV light depends on several factors:
- Light intensity I [W]
- Exposure time t [s]
- Surface area A which is illuminated [m²]
The disinfection dose D can be calculated from these parameters, by using the following formula:
- D = I x t / A [Ws/m² = J/m²]
(Literature sometimes uses mJ/cm², where 1 mJ/cm² = 10 J/m²)
The exact dose needed for disinfection can be obtained from literature or various microbiological studies, and it depends on the following:
- Target level of disinfection (e.g., 99.99%, 90%)
- Properties of the particular microbial culture
UV-C: The Disinfection Industry Standard
The UV-C band of the spectrum does not come from the Sun, because the Earth’s ozone layer blocks most of it. However, it can be produced by artificial light sources (mercury tubes, welding arcs, specialized UV LEDs). Having the shortest wavelength (100 to 280 nm), it carries the most energy in the UV spectrum, which makes it the most potent disinfectant. UV-C radiation directly attacks the RNA or DNA of microbes and alters it so that they can no longer replicate.
Because of their ability to produce light in the UV-C spectrum, mercury tubes are widely accepted as a de-factostandard in the UV disinfection industry. The UV emission of mercury tubes peaks at 254 nm, with good (but not optimal) overlap with the absorption spectrum of DNA/RNA molecules. When it comes to LED-based solutions, recommendations are to use UV-LEDs that operate at 275 to 280 nm. However, the critical DNA/RNA absorption peaks at the wavelength of 265 nm and goes down to about half of this level for 280 nm, in the worst case. Therefore, the dosage calculations have to be corrected accordingly, by multiplying D by the factor of 1 to 2. On the other hand, this type of UV-LEDs has superior efficiency and lifetime compared to UV LEDs working at 265 nm or shorter wavelengths, representing a good compromise for most applications.
However, UV-C light has the same effects on the human cell DNA as to any other DNA molecule. Therefore, some precautions must be taken while working with UV-C light to minimize the risks: all exposed parts of the body should be covered, or otherwise protected. For this reason, the use of UV-C light is restricted in public and open spaces, which is the main limiting factor for using it in a broader range of applications. A typical 99,99 % Disinfection dose, e.g., for E-Coli, is 400 to 800 J/m², whereas the working place limit for one workday is 30 J/m² for 270-280 nm.
UV-A & Blue Light Disinfection
Although there is no UV-C radiation from the Sun reaching the Earth, Sun exposure can be used effectively for disinfection, suggesting that some other wavelengths such as the UV-A and blue light, also have some disinfectant properties. The UV-A/blue light disinfection mechanism is based on oxidative stress and the formation of short-term radicals. These highly reactive particles attack the pathogen as a whole and have detrimental effects on its DNA/RNA molecules. The example of solar water disinfection (SODIS) in third-world countries near the equator, where the sunshine is abundant, clearly illustrates this phenomenon. Moreover, blue light disinfection is a major contributor to the so-called “spring effect,” the beneficial effect that the spring and summer periods have on the immunity and disease resistance (See also: https://en.wikipedia.org/wiki/Solar_water_disinfection; Solar Water Disinfection (SODIS) refers to the blue light to UV-A radiation and mild heat.
Since the Sun is a powerful natural light source that delivers more than 100 W/m² of blue and UV-A light, the required dose for disinfection with blue light is significant, in the range of MJ/m². Because blue and UV-A light is part of the natural spectrum, compatibility with humans and materials is much higher than for the UV-C light. Nevertheless, human safety and material durability aspects must be investigated in designs using UV-A/blue light, as well.
The Spring Effect
The UV-A/blue light disinfection is a significant contributor to the so-called spring effect: viral infections such as influenza are usually suppressed during the spring and summer. Therefore, a significant reduction in SARS-CoV 2 virulence is expected under normal conditions. When non-confined people go out in nature during warm weather, the sun inactivates pathogens such as the shelled viruses (e.g., influenza, SARS-COV-2) in the aerosols. Together with significant dilution by ventilation or wind, the probability of infection during the summer is reduced in such conditions.
In the western world, we know about the efficiency of the spring effect against influenza and cold from our personal experience. However, there are still controversial scientific discussions about this multi-factor phenomenon. In any case, keep in mind that advanced LED lighting solutions will undoubtedly contribute to bringing this spring effect into buildings and help flatten-out the second wave next winter.
When illuminated, some metal oxides such as TiO2, tend to oxidize any organic material that gets in contact with their surface. Not only small molecules like odors and hazardous gases can be removed from the air by such metal oxides, but also pathogens, which get attacked and inactivated. Depending on the photocatalytic material used, wavelengths in the range from 365 nm and even up to 475 nm are well-suited to trigger the effect. For example, just one hour of exposure to a 1000 lux white light source may be enough to achieve a disinfection ratio of up to 99.8%. UV-A and BlueLight irradiation in combination with Photocatalytic surfaces can achieve similar disinfection efficiency ratios as conventional UV-C light, but without the harmful effects that UV-C has on human health. Experts from the EBV Lightspeed team are firmly convinced that this effect may be a break-through in surface disinfection, providing high compatibility with a wide range of materials and ensuring low hazard to human safety.
A thin layer of photocatalytic metal oxides can also block the UV light, preventing it from penetrating to the underlying material. For that reason, metal oxides such as the TiO2 are typically used as UV blockers in various sun lotions and sunscreens, protecting the skin from sunburns. TiO2 can also be used with equal success to protect some other materials against UV-degradation (e.g., ABS plastics).
UV-LED Solutions and Application Examples
As already mentioned, mercury tubes are the de-facto standard in the UV disinfection industry. However, having been used in industry for a very long time, mercury tubes have reached their design peak and can no longer be significantly improved. Therefore, some new solutions provided by the emerging wide-bandgap semiconductor industry will inevitably replace traditional mercury tubes and lamps in the foreseeable future.
Even today, there is a broad range of UV-LED devices that offer superior performances. Although they still struggle with a high degree of power, the main advantages of LED sources are their small size and semiconductor properties. UV-LED based solutions are especially attractive for small and flexible applications. Moreover, UV-LED sources allow for more efficient optical design, allowing them even to outperform mercury tubes for some specific applications. Unlike mercury tubes, UV-LEDs do not take warm-up time and can be dimmed with PWM signal, just like the regular LEDs. The heat management is much simpler than for the mercury tubes. The typical forward voltage of UV-LEDs ranges from 5 to 8 V, allowing installation without the need for HV protection, and driving by the existing LED driving IC solutions. This especially applies to wet areas with more strict electrical safety regulations (VDE 100: max. 12 V AC or 30V DC).
UV-LEDs open up some new possibilities for the design of very efficient disinfection devices, such as the water reactors. By precisely controlling the amount of UV light through PWM dimming, in relation to the flow of water through the reactor, it is possible to obtain optimum disinfection performance, while achieving significant power reduction. Another good example of applications for which UV-LEDs are perfectly suitable is small home appliances, where low power LEDs with 20 mA disinfect small distinct areas over long periods. Thanks to their small size, UV LEDs can be used in cosmetic holders, toothbrush cases, and similar devices, providing 24/7 disinfection while consuming only a minimum amount of energy (in the range of mW), a feat unattainable by any other means.
After a period of reduced virulence due to the previously mentioned spring effect, the COVID-19 virus is expected to make its comeback in the fall. Some of the current COVID-19 hotspots are cooled workplaces in e.g., the meat-processing industry (Tönnies in Germany operates in a winter climate of 5 – 10 °C and with untreated ventilation; Source – German). With the decreasing temperatures in the fall and winter period, it is suspected that the virulence of COVID-19 will get back to the previous level, thus facilitating the large-scale spread in the second wave.
So, let us now work on UV-LED solutions in order to bring the spring effect in buildings as a Corona “fallback” solution. We need to prepare now to make the corona fall back as smooth as possible – we need to recharge and to have the strength for the Corona comeback at the fall/winter time!
What is needed to make it real?
- Find the right approach for your application
- Design the solution
- With the help of EBV support, we can make it real!
EBV Elektronik, as the largest Semiconductors distributer in the EMEA region, offers a comprehensive portfolio of various LED/UV-LED solutions, along with supporting electronic components. Additionally, EBV’s team of lighting experts offers consulting and knowledge related to the latest technology, as well as access to a network of partners in science, qualifications, and industry. For further details, please join our free on-demand webinars:
Alternatively, contact us at EBV directly, for further support.
We are looking forward to fighting COVID-19 with you and welcome you to our registered webinars for virtual meetings. Until then:
- Go out (keep the distance) and enjoy the sun, as the most natural source for pathogen removal
- Stay healthy!
Dr. Dieter GROSS, Business Development Manager for Light, Home & Building, EBV Elektronik
Darko ILIJEVSKI, Technical Editor & Editor, EBV Elektronik