In which aspects of COVID-19 prevention and control can deep-ultraviolet LEDs play a role in disinfection?
Ultraviolet radiation can be divided into several bands: UVA, UVB, UVC and UVV. The band of ultraviolet radiation capable of sterilisation is UVC. Currently, there are two main types of UVC sterilisation devices available on the market: low-pressure mercury lamps and UVC LEDs. The ultraviolet germicidal lamps we commonly refer to are low-pressure mercury lamps, which are widely used. In recent years, UVC LEDs have also demonstrated good efficacy in surface disinfection and sterilisation, and hold significant potential for further development. As a new method of sterilisation and disinfection, UVC LEDs can address certain issues that traditional low-pressure mercury lamps are unable to resolve. Shenzhen Deshengxing Electronics Co., Ltd. will continue to provide updates on the latest developments in UVC technology.
Broadly speaking, there are various types of mercury lamps, such as low-pressure mercury lamps, high-pressure mercury lamps and mercury vapour lamps. Classified by wavelength, their sterilisation principles can be categorised into three types: One is the 185 nm mercury lamp, which converts oxygen in the air into ozone and utilises ozone’s strong oxidising action to kill bacteria effectively and without leaving any dead spots; however, its drawbacks are quite evident, the ozone produced by 185 nm ultraviolet germicidal lamps strongly irritates the human respiratory tract, potentially causing a sore throat, chest tightness and coughing, and triggering conditions such as bronchitis and emphysema. The second method utilises a 254 nm mercury lamp, which sterilises by directly irradiating the DNA and RNA of microorganisms; this works on the principle that UVC wavelengths can damage the chromosomes of microorganisms. The third method employs photocatalytic technology using ultraviolet light in the UVA band. Deep ultraviolet (DUV), which has a shorter wavelength than standard ultraviolet light, is currently being used in a variety of sterilisation and disinfection applications, including healthcare and public spaces. In terms of light sources, the market is currently dominated by ultraviolet mercury lamps and deep ultraviolet LEDs.
To date, over 5,000 UV disinfection units have been delivered to the Leishenshan and Huoshenshan Hospitals. It is reported that the first batch of UV disinfection units comprised hundreds of disinfection vehicles and over a thousand UV disinfection lamps; the disinfection vehicles will be used to transport patients, whilst the UV disinfection lamps can be utilised in various post-operative disinfection scenarios.
During this pandemic, whilst UV disinfection vehicles and lamps have been deployed directly at the epicentre of the outbreak, and whilst people like you have purchased mercury-based UV lamps for indoor disinfection, the most widely discussed topic among the public—given the shortage of face masks—has been the use of UV lamps to disinfect masks in order to extend their lifespan.
Due to factors such as low cost and mature technology, mercury lamps currently dominate the market for most products used in water treatment, industrial disinfection, hospital disinfection and indoor disinfection. However, from a long-term perspective, with the entry into force of the Minamata Convention, UV mercury lamps—which contain mercury—will gradually be phased out.
The Current State of Deep-Ultraviolet LED Disinfection and Its Role in the Pandemic Response
In the same way as 254 nm mercury lamps are used for sterilisation and disinfection, deep ultraviolet LEDs (UVC LEDs) primarily utilise the 200 nm–280 nm wavelength range to cause radiation damage to microorganisms (such as bacteria, viruses and spores) and to destroy their nucleic acids, thereby killing them and achieving the purpose of disinfection. Although UVC LEDs are currently still in their infancy, and their cost-effectiveness and luminous efficiency still fall short of those of mercury lamps, UVC LEDs, with their safety, environmental friendliness, compact size, high efficiency, low power consumption and the absence of chemical residues, have already found widespread application in portable surface disinfection, the maternal and infant care market, and static water treatment.
Health and hygiene standards in public spaces and for everyday household items are constantly rising, and UVC LEDs can play a significant role in this area. For example, in a project where Guoxing UVC LEDs were used in collaboration with a renowned international home appliance manufacturer to develop a humidifier, the application of UVC LED modules in the device prevented the growth of bacteria in water left standing for long periods, thereby ensuring a hygienic home environment. At the same time, there are numerous portable UVC LED sterilisation and disinfection products available for everyday items such as tableware and nappy bags. In hospitals, items used by medical staff—such as infrared thermometers, stethoscopes, blood pressure cuffs, mobile phones and spectacles—can also be disinfected using UVC LED sterilisers.
It is worth noting that, the RNA structure of most viruses is relatively simple, and the use of UVC LEDs at appropriate doses can effectively inactivate the corresponding pathogens (2019-nCov, being an RNA-replicating virus, is more difficult to treat). Particularly in healthcare settings, UVC LEDs offer broad-spectrum disinfection, effectively inactivating common viruses and bacteria, and represent a highly efficient and convenient disinfection solution. Essentially, common live viruses can be efficiently inactivated; once the required illuminance or light power is achieved, inactivation occurs within a few seconds. However, hospital UV lamps are relatively slow at disinfecting air in large spaces, though this should not take more than two hours. During the SARS outbreak, a research team led by Dong Xiaoping from the Institute for Viral Disease Prevention and Control at the Chinese Centre for Disease Control and Prevention discovered that the SARS virus is sensitive to thermal radiation and UVC. Researchers found that exposing the coronavirus to UVC irradiation at an intensity greater than 90 μW/cm² could inactivate the SARS virus within 30 minutes. This explains why, in recent years, UVC has been increasingly utilised in the field of healthcare disinfection, as well as in water and air treatment.
This also goes a long way towards explaining why, when a major outbreak occurs again, so many people—like yourself—are taking an interest in UV disinfection methods and the role of UV LEDs in public protection. According to the newly published ‘Rapid Guide to the Diagnosis and Treatment of Novel Coronavirus Pneumonia’, 75% alcohol, diethyl ether, chloroform, formaldehyde, chlorine-based disinfectants, peracetic acid and ultraviolet light can all inactivate the virus.
It is believed that, when combined with other protective measures, UVC can, to a certain extent, effectively prevent and control the spread of the 2019-nCoV outbreak. The entire UVC LED industry chain is also bound to accelerate trials and research into the use of ultraviolet irradiation for sterilisation against the novel coronavirus.
At present, for portable sterilisation devices and small household appliance sterilisers, the UVC LED’s light power, exposure time and beam angle vary depending on the specific usage environment. For example, in the case of some compact, portable sterilisation devices—which are primarily used on items that come into frequent contact with us in daily life, such as mobile phones and cutlery— for these, irradiation with a low-power UVC LED (2–5 mW) for a few seconds to several tens of seconds prior to use is sufficient; whereas for sterilising water cups, due to their slender structure, the UVC LEDs must be designed with a beam angle of 60 or 30 degrees to ensure a longer irradiation distance, whilst also accounting for the attenuation of the UVC spectrum in water; such products generally utilise units with a light output of around 10 mW; Furthermore, in low-flow water dispensers, the light output generally needs to be 50–100 mW or even higher. However, as higher power output leads to higher costs, some manufacturers currently combine centralised filtration and disinfection methods, installing UVC LED disinfection modules only at the final stage of the water outlet; this significantly reduces costs.
Therefore, from a purely current perspective, mercury-based UV lamps remain the primary technology used in water treatment, industrial sterilisation, hospital sterilisation and indoor sterilisation, whilst UVC LEDs can play a significant role in household appliances and portable sterilisation and disinfection devices, which will be highly effective in reducing and containing the spread of viruses and bacteria in the home and in public places.
In the long term, as mercury lamps gradually fade into history, UVC LEDs will continue to evolve towards higher power and greater luminous efficacy, whilst their wavelengths will continue to shift towards the lower spectrum. This will place higher demands on the packaging of UVC LEDs, and how to further improve heat dissipation and UV resistance will be a key challenge. Currently, the most common packaging method on the market involves bonding quartz glass to a cavity using UV-resistant adhesive. Whilst this approach poses few problems in certain operating environments given the current low luminous efficacy, as luminous efficacy and brightness increase, all-inorganic packaging appears to be the optimal solution for UVC LEDs at present. Guoxing Optoelectronics has already developed samples of all-inorganic packaging and will conduct further batch trials. At the same time, the company is comparing several all-inorganic packaging methods in an effort to develop the optimal all-inorganic packaging product. Overseas, a rather specialised type of fluororesin has in fact already been developed, which exhibits excellent resistance to UVC; however, its encapsulation process is complex and is not yet suitable for mass production. Should significant progress be made, resin encapsulation is likely to carve out a niche in the market in the future.
