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Surface‑mount UV LEDs, integrated into laboratory surfaces and equipment, can reduce the spread of infection
The sterilisation of air, water and surfaces is key to preventing viruses and bacteria from spreading. Ultraviolet (UV) LED technology has a pivotal role to play in the fight against the SARS-CoV-2 (Covid-19) virus, as well as other pathogens.
According to recent research from French tech media company Yole Développement, the UV LED market is growing at an unprecedented rate, mainly due to the current pandemic. It is expected to be worth $2.5bn in 2025 (up from just $144m in 2019).
UV LEDs have become increasingly popular because they have proved effective in neutralising all bacteria and viruses, including the Covid-19 virus. The reason is simple.
Natural UV radiation
The natural UV radiation of sunlight is absorbed by the ozone layer in the Earth’s atmosphere. Consequently, no living organism, including viruses and bacteria, has developed resistance to UV rays.
Not only are UV LEDs highly effective, they also eliminate some of the main challenges and risks that are associated with other, more traditional sterilisation methods.
Existing sterilisation technologies have limitations, however. Different methods and technologies can be deployed to disinfect air, water, and surfaces, which can either be passive or active.
Passive methods include high‑efficiency particulate air (HEPA), activated carbon and ceramic filters. These technologies are effective in retaining pathogens and pollutants but are unable to destroy them; the risk of contagion cannot be eliminated entirely. In addition, they require frequent maintenance.
Another common passive method is the use of chemical products such as chlorine. The main risk here is that pathogens may develop resistance over time. Additionally, chemicals only work in static situations and can produce harmful volatile hydrocarbons.
Like UV light-emitting devices, ionisators and plasma systems are active methods that are used to combat viruses and bacteria. The main downside to these active systems is that they produce ozone, which is harmful to human health.
Mercury lamps vs LEDs
A surface mount UV LED
on a hexagonal metal core PCB
Until the arrival of LEDs, the main way of generating UV rays has been the use of mercury-based radiation sources. Such UV emitters include low and medium-pressure mercury vapour (Hg) lamps that emit UV light in a spectrum of 185‑405nm through gas discharge.
UV light can also be generated using UV cold cathode tubes (UV-CCL or UV lamps) in a spectrum of between 185‑405nm through glow discharge.
New international legislation which came into force in January 2020, means that mercury-based lamps are, with very few exceptions, no longer an option. The manufacture, import, and export of mercury lamps is now banned under an international treaty, the Minamata Convention on Mercury.
UV LEDs are the only viable alternative to traditional UV‑based disinfection methods. The mercury‑free technology means they are compliant with the Minamata Convention and eliminate the need for mercury disposal.
Compared to mercury vapour lamps, UV LEDs bring other important benefits. They deliver a more consistent UV spectral output for a given temperature and cover a broader range of wavelengths, which translates into greater flexibility. They also tend to be smaller, more robust and – perhaps more importantly – more energy‑efficient.
UV LED types
UV LEDs emit UV rays in the 227-405nm spectrum through electroluminescence.
There are three main wavelengths: UVA, UVB, and UVC.
With a wavelength of 315‑400nm, UVA LEDs offer greater penetration than UVB and UVC rays in dispersed biological tissue such as human skin. The main applications of this technology include dentistry and cosmetics. They are also used to cure resins, adhesives and paints in the industrial sector.
With a wavelength of 280‑315nm, UVB LED rays encourage the formation of vitamin D in the human body. This technology is often deployed in medical applications such as phototherapy and dermatological treatments.
UVC LEDs also have particularly short wavelengths (between 260‑270nm) that offer the greatest sterilisation effect.
Multi-UV LEDs are now being developed, which will offer even greater flexibility.
UVC LEDs key considerations
Micro-organisms come in different shapes and sizes and react differently to UV radiation.
Choosing the right radiation intensity is paramount. It is also important to remember that different materials reflect UV rays differently, which needs to be considered at the design stage.
The intensity of UV radiation is inversely proportional to the square of its distance; the greater the distance from the radiation source, the lower its intensity. To be effective, the emitter should be as close as possible to the area that needs to be sterilised.
The beam angle is another important consideration, which is where lenses are used. Lenses reduce the irradiated surface and increase the radiation energy per square metre, meaning that, with the same energy output, the exposure time required is reduced.
The use of different UV lenses with compatible glasses enable users to scale the irradiation output easily according to the application.
Consider geometry
Viruses such as Covid-19 are airborne, so UVC LEDs can be particularly effective when installed in HVAC systems.
In addition to radiation intensity, air flow rates and geometry are a key consideration here. An air duct at the outlet of a fan can help to stabilise the air flow, offering an ideal location for UVC LED installation.
It is also vital to bear in mind that intense UV light with wavelengths over 254nm can be harmful to human skin and eyes.
A less intense UVC light (207‑222nm), applied within the current regulatory exposure limits (~3mJ/cm2/hour), can neutralise most airborne pathogens without damaging exposed human tissue.
Strikingly, this UVC wavelength can achieve 99.9% viral inactivation in only 25 minutes.
Viruses and bacteria, including influenza, noroviruses, rotaviruses, streptococcus, and salmonella, are also transmitted via surfaces. Different UVC LED technologies are available to disinfect surfaces of different sizes, from the smallest to the largest.
Low-power UVC LEDs with outputs of 2‑4mW and 20mA can be a good choice for larger surfaces, while for smaller‑scale applications it may be preferable to opt for a compact, mid‑power UVC LED.
High-power UVC LEDs, with DC power consumption of 100mW at 250mA are a great solution to treat drinking water and disinfection of water pools.
UVC LEDs and Covid-19
UVC LEDs are already playing a major role in the fight against Covid‑19. One example is to protect frontline healthcare workers.
For example, a disinfection tent fitted with UVC LEDs was set up to disinfect the protective clothing of the medical staff at the Huoshenshan Hospital in Wuhan, China.
This is used to protect workers and prevents the virus from spreading outside the hospital. UVC emitters were fitted to the reflective surfaces of the ceiling, walls, and flooring.
During the 30-second disinfection process, the UVC LEDs provide a dosage of 6mJ/cm2 with a consistent brightness of 200μW/cm2.
The light wavelength of 265‑280nm destroys genetic information, ensuring that the virus can no longer spread or infect other cells.
UV LEDs are key to preventing the spread of pathogens. They are a reliable, energy-efficient, and highly‑effective sterilisation solution that overcomes some of the main limitations of other disinfection methods.
There is a broad range of UVC LEDs available, covering a variety of wavelengths and power outputs. With the development of multi-UV LEDs, we can expect this technology to become commonplace across an even broader range of applications.
