While disinfection solutions have always been there but the recent corona pandemic has lead to some serious effort in the development of powerful disinfection solution. Osram team has also been working in this direction. Two engineers at Osram– Hans Lugauer and Aleander Wilm – who have been spearheading this development work are of the opinion that UV-C LED can be the potential disinfection solution for such bacteria and viruses. However, use of UV-C LED for disinfection seems quite promising but has its own set of challenges.
Short wave low pressure discharge lamps have been conventionally used to sterilize and disinfect water, air and surfaces. But future of disinfection applications lies in using UV-C LED. This is because LEDs are compact and flexible, can be switched on or off quickly and are resistant to vibrations.
There many new applications that can be developed using UV-C LED such as mobile disinfection device that can fit in your pocket. The engineer duo named it as “germ killers“. But despite having so much potential, this application still doesn’t exist in commercial form. This is because of safety issues in using UV-C LED apart from efficiency problems.
UV-C is quite harmful for human skin and eyes. So while disinfecting the uniform of an employee, he is expected to wear special face masks and gloves that are impermeable to UV-C radiations. Robots that are used to disinfect the floors are sensor driven. They get automatically switched off, as soon as the sensor detects presence of a human being in certain range.
UV-C LED is a better choice than mercury lamps for disinfection because it is more workable in situations of tight space, vibrations or shock etc. Also preventing glass breakage and mercury from escaping is quite a challenge in itself.
UV-C LED can have multiple applications – for eg. it can be used to disinfect taxis, shared cars, buses etc. Lot of applications will come up as soon as this solution is developed with improved performance at reasonable costs.
But what makes UV-C LED so effective against bacteria, viruses and other microorganisms?
There is no natural UV-C available on earth’s surface as it gets absorbed by the ozone layer. Therefore the microorganisms have not developed any defense mechanisms against UV-C radiations.
Destruction of DNA (also RNA) via UV-C radiation
Short wave UV-C radiation (200-280 nm) is part of UV radiation that has maximum energy. So light below wavelengths of 280 nm break the chemical bonds in the RNA/ DNA helix of the bacteria or virus i.e. it tears apart its genetic information, thus rendering micro-organisms incapable of reproducing. In such a condition, the bacteria/virus cannot cause any infection.
But the necessary dose of UV-C required to kill the microorganism depends on its type. Maximum disinfection effectiveness is achieved at around 265 nm wavelength. UV-C LED effectiveness is directly proportional to the wavelength. So optimization of wavelength results into UV-C effectiveness.
UV-C LED has quite an innovative material system. It consists of AlGaN (aluminum gallium nitride), which is quite similar to InGaN (indium gallium nitride), which is used in blue and green LED. Therefore, all the manufacturing processes of chip making are applicable, except epitaxy process of growing tiny crystal layers, which is significantly different in this case. To produce AlGaN semiconductor crystal in epitaxy, higher temperatures are required (about 1400 degree Celsius) and for this special manufacturing plants are required.
Special encapsulation material is also required to increase the light output from chip to be used in LED package. Silicone is commonly used in similar cases, but it decomposes quickly due to high energy UV-C photons exposure. So a new material that doesn’t decompose and yet provide sufficient transparency needs to be developed. Once the production processes and material issues are resolved, efficiency and reliability issues need to be addressed.
Prototype of a UV-C Package
Lot of development work is required to reach the stage where UV-C LED can be mass produced at reasonable costs. However, LED was also considered expensive & difficult to produce at commercial level about 10 years ago, but now we have achieved that level for LED. Similarly, it is not impossible to mass produce UV-C LED economically, in the near future.