Purifying air, surfaces & water with UV light
01 May 2022
The invention of the mercury lamp roughly 100 years ago revolutionised medical sterilisation. To this day, UV rays play a key role in the disinfection & sterilisation of surfaces, interior spaces & even water – even more so since the outbreak of coronavirus & the COVID-19 pandemic.
This article was originally featured as the cover story in the May 2022 issue of EPDT magazine [read the digital issue]. And sign up to receive your own copy each month.
Here, Alain Bruno Kamwa, Product Sales Manager, Opto at electronic component distributor, Rutronik & Nancy Yang, Sales & Marketing Engineer at opto-semiconductor specialist, Lextar explain how UV-C LEDs open up numerous new possibilities…
Respiratory droplets, contact and aerosols are the main routes of transmission of COVID-19. The sterilisation of surfaces and air – along with vaccination, testing and general COVID-19 safety rules – is therefore a key contributor to slowing the spread of the pandemic.
Figure 1. Overview of UV-A, UV-B & UV-C rays and their technologies, target markets & applications
A variety of methods are available for this purpose. One of the simplest is direct irradiation using UV lamps, such as those used in hospitals. It offers good sterilisation efficiency, but also has a few shortcomings: firstly, nobody can stay in the room during sterilisation, as the UV rays are liable to cause various health issues if they hit the body. Secondly, a large amount of UV energy is required for effective sterilisation. This is because the UV-C rays suitable for sterilisation (Figure 1) are greatly attenuated during transmission: the dose rate on a given area decreases with increasing distance from the radiation source inversely proportionally to the square of the distance (Figure 2). Thus, this method is not really suitable for public places.
Hidden air purification
Modern UV-C LED light sources are opening up new possibilities, as compared to mercury lamps, since they guarantee higher energy density and lower power consumption with exactly the same volume characteristics. And based on their small size, they are easier to integrate and allow ‘hidden’ UV sterilisation products. They take up very little space and do not need to be cleaned separately. On the downside, there are higher costs and limited luminous efficacy. The light output of a single LED is usually still in the milliwatt range. Therefore, it is unable to purify the air by irradiating a large area like a mercury lamp tube can. As a result, UV-C LEDs are combined with other methods to kill airborne bacteria.
Current methods include air recirculation, a photocatalyst, UV-A LEDs, a high-efficiency HEPA filter and a UV-C LED sterilisation system. A fan is usually used to generate air circulation, which circulates the room air and drives the bacteria and viruses suspended in it to the filter element in the disinfection chamber. They accumulate on the surface of the filter element. Unlike traditional air purifiers, they not only collect here, but are also rendered harmless by the UV-C LED. With this particular method, the radiation remains inside the device; meaning people do not have to leave the room during sterilisation.
Figure 2. UV-C radiation decreases with increasing distance from the light source
The Lextar LBM2101 UV-C LED air sterilisation module can be integrated into air purifiers, air conditioners and other compact end devices, as it measures just 27 mm in diameter and 12.7 mm in height. Its special design concentrates the UV rays emitted by the LED inside the device (Figure 3). This increases the effectiveness of UV-C radiation and ensures that the radiation does not escape. After just one hour, the sterilisation rate reaches more than 99%, in other words, more than 99% of the airborne viruses and bacteria are rendered harmless. The aluminum housing ensures excellent heat dissipation, thereby extending the service life of the LED.
Driving without risk of infection
Coronavirus survives in the air for up to three hours, and longer indoors than outdoors. To reduce the risk of infection in public transportation, including taxi cabs, car-sharing vehicles, buses and trains, Lextar has developed an automotive UV-C LED air sterilisation module. It can be combined with the vehicle’s air conditioning system without impacting its operation and destroys 99% of the SARS-CoV-2 pathogens.
Figure 3. With three reflectors per UV-C LED, the matrix generates particularly high-energy UV-C radiation
The module consists of a UV-C LED matrix in which each of the 20 LEDs is equipped with three reflectors, thus generating particularly high-energy UV-C beams (Figure 3). Further, there is a nanoscale filter that removes 99.53% (tolerance ±10%) PM2.5 from the air, improving indoor air quality immensely. The module is compatible with current auto-filter systems, meaning it can be replaced without modification and adapted according to customer requirements (Figure 4).
Sterilising water with light
As well as air, UV-C LED sterilisation and disinfection modules can be used to disinfect surfaces and water. When it comes to the latter, a distinction needs to be made between flowing and standing water. In tanks for water purifiers, or in water tanks for humidifiers, the purified water usually stands for a long period of time, thus allowing bacteria from living organisms in the air or on surfaces to multiply significantly. Lextar’s static water sterilisation modules regularly irradiate the water in the tank with sufficient radiation power to kill the bacteria.
The best sterilisation rate can be achieved if the module is installed at the bottom of the water tank and the UV-C rays hit the water directly through a window in the waterproof module housing. However, the sterilisation module can also be placed on the side or on top of the water tank.
Figure 4. The automotive UV-C LED sterilisation module can be integrated into the air conditioning system of a vehicle
The sterilisation of running water is quite a different proposition: it flows relatively quickly through the pipeline – and also through the sterilisation module. So there is obviously only a very short space of time to completely destroy the bacteria. This requires a very high level of radiation power, which also leads to higher costs than for standing-water sterilisation modules. This is the reason why such modules are currently found mainly in high-quality household water dispensers and in commercial machines.
The installation location of the module is not as critical here as it is with standing water. But what should be considered is the length of the water outlet pipe. Since secondary contamination can occur in the water pipe, the shorter the distance from the water outlet of the module to the water outlet of the unit, the better.
UV light, a true all-rounder
Figure 5. The water treatment module can be used for running water with a flow rate of between 0.6 & 12 l/min
Thanks to their sterilising effect, UV-C LEDs have experienced a huge surge in demand as a result of the COVID-19 pandemic. But there is more to UV light than just sterilisation. For example, it can be used to neutralise unpleasant odours, enable fruit and vegetables to grow without natural sunlight and keep produce fresher for longer after harvesting. It can accelerate the drying and curing process of plastic coatings or paints, for example, and detect the composition of pharmaceutical drugs via spectroscopy.
For such applications, Rutronik offers all the necessary components – from UV lamps, modules, lenses and LED drivers to fans for thermal management and control sensors, for example, for UV, VOC (volatile organic compounds) and PIR (passive infrared sensors). Furthermore, Rutronik has developed two boards: the first is an evaluation board that uses a VOC sensor to detect odours and neutralises them with UV-A LEDs plus a photocatalytic filter; the second board enables the sterilisation of air, water and surfaces with the help of UV-C LEDs.
The difference between disinfection & sterilisation
Figure 6. Germ-free water straight from the faucet: the Lextar faucet UV-C sterilisation module, with a power consumption of 10 to 30 W, cleans at a flow rate of between 2 l/min & 12 l/min
Disinfection reduces the number of germs that can cause disease to such an extent that there is no longer any risk of infection.
During sterilisation, all microorganisms, such as bacteria, fungi, spores or viruses, are removed or killed in all their stages of development.
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