UV sterilized light and trend of UV light source

With the global spread of COVID-19, various protection methods and disinfection technologies have attracted much attention. Medical alcohol, disinfectant, and ultraviolet radiation are all products and methods to prevent and control the spread of the new corona virus.

Compared with chemical disinfection, what is the performance and safety of UV radiation disinfection technology? With the continuous development of UV LED technology, ultraviolet solid light source with UV mercury lamp, are there differences in application scenarios between them?

What are the difficulties and pain points that need to be solved in the advancement of UV LED in the application field? The above issues are closely related to the subsequent development of UV LED.

We will analyze these aspects for your reference.

  1. UV disinfection technology

Ultraviolet rays are between the visible light band and X-rays. According to the wavelength, ultraviolet rays can be subdivided into near ultraviolet (UVA: 315-400 nm), mid-ultraviolet (UVB: 280-320 nm), and deep ultraviolet (UVC: 200-280 nm) ) And vacuum ultraviolet (VUV: 10~200 nm), the ultraviolet energy in the UVC band is the highest, but due to its shortest wavelength, it is absorbed in the atmosphere, resulting in serious attenuation. It is almost not in the near-Earth solar spectrum. The ultraviolet light with this band is also called the “sun blind” ultraviolet band.


Ultraviolet light to microorganisms inactivation is not complicated. It mainly utilizes the absorption of ultraviolet rays by the nucleic acid of microorganisms, destroys its nucleic acid function, stops the microorganisms from copying, and realizes disinfection and purification.

You maybe not knowing that not the entire ultraviolet band has the function of inactivating microorganisms. Among them, only the UV light in the 240-260 nm range in the UVC band is easily absorbed by bacteria and effectively acts on the bacterial DNA, which interferes with its replication, causes the death of bacteria , and UVA & UVB are outside the range of the microbial absorption peak, so the sterilization efficiency is very low.

There are no chemicals involved in the reaction during the UV disinfection process, and no disinfection by-products are produced. The data shows that under the condition of UVC irradiation intensity of 30 mW/cm2, nearly 100% inactivation of most bacteria can be achieved within 1s.

Therefore, UV disinfection technology is a physical disinfection method, which has the advantages of broad-spectrum, high efficiency, fast , environmentally friendly, harmless, simple and easy to operate.

The application of UV rays in the field of disinfection has a long history. As early as the 19th century, Downes and Blunt’s research mentioned that UV light has the effect of disinfection. Danish scientist Finsen then applied UV rays to the field of medical and health care.

It shows that ultraviolet disinfection technology has long been recognized and applied by humans. The “New Coronavirus Pneumonia Prevention and Control Plan” mentioned that the new coronavirus is sensitive to ultraviolet light and heat. Therefore, in the prevention and control of the epidemic, in addition to chemical disinfection technologies such as medical alcohol and chlorine-containing disinfectants, UV disinfection technology, which is one of the physical disinfection methods, is also recognized by relevant agencies.

At present, the application scenarios of UV disinfection technology are mainly in specific places such as factories and hospitals, and it is not popular in families.

In addition to factors such as the size of UV disinfection equipment, photo biological safety concerns are also an important factor affecting and limiting the application of such products. This concern is mainly due to the possible damage to human eyes and skin caused by ultraviolet radiation.  It should be noted that under the premise of ensuring a safe dose, UV rays are difficult to cause damage to human skin and are also beneficial to human health under certain conditions.

For example, UV radiation in sunlight can promote the production of vitamin D in the human body. Encourage babies and young children to sunbathe properly, but excessive sun exposure may cause the skin to darken and should be avoid.

In summary, we need to use the UV disinfection technology in a scientific and standardized manner in conjunction with the characteristics of the UV light source and the product description.

Under the premise of meeting the safe dosage, the UV disinfection method is feasible and beneficial. In addition, with the LED light source’s small size, easy integration, and fast switching, combined with mature sensing technology and control technology, it can effectively avoid safety hazards caused by improper use of UV rays. Therefore, under the premise of ensuring safety and reliability, UV disinfection technology can be fully utilized to serve humans.

2. Comparison of UV light sources

In the process of inactivating microorganisms, UV rays in the wavelength range of 240 to 260 nm are mainly used. Common UV disinfection products are mainly based on the UV output from low-pressure mercury lamps. With the continuous development of nitride material technology, UV LEDs based on high Al component nit rides are gaining attention.

By comparing the characteristics of the two light sources, it is helpful to understand the performance difference between solid-state light sources and UV mercury lamps in the field of disinfection.

The efficiency of UV disinfection technology is mainly influenced by the output wavelength of the light source and the UV irradiation dose.In 2011, a research team from the Technical University of Berlin designed and prepared UV LED light source modules based on 269 nm and 282 nm, and conducted inactivation experiments on Bacillus subtilis in water using these two different wavelengths of UV solid-state light sources.

The results showed that 269 nm had a more complete inactivation effect on Bacillus subtilis at the same UV irradiation dose.In 2016, the research team at Seoul National University studied the inactivation efficiency of UV LED and low-pressure mercury lamp on E. coli and Salmonella. The results showed that the UV LED with a peak wavelength of 266 nm significantly outperformed the low-pressure mercury lamp in killing both bacteria under the same irradiation dose conditions.

The above experimental results indicate the existence of a correspondingly most efficient wavelength for UV inactivation of a particular microorganism.

The output wavelength of the UV LED can be set by tuning the composition of the material in the active region, and the half-peak width is narrow, at about 10 nm. Thus, the output wavelength of UV LEDs is arbitrarily adjustable between 200 and 365 nm, covering the range from UVA to UVB.

But for UV mercury lamps, the spectral range of this light source is wide and not adjustable, e.g., low-pressure UV mercury lamps mainly output UV near 253.7 nm. The wavelengths and doses required for inactivation of different microorganisms vary greatly, making it difficult to identify and distinguish which specific wavelengths are most efficient for inactivation of certain microorganisms in practical UV disinfection studies using mercury lamps.

In addition to greater output wavelength flexibility, the small size of UV LEDs, compared to mercury lamps, makes it easy to create multiple wavelength modules in an integrated package, enabling researchers to develop highly efficient disinfection light sources.

The UV irradiation dose is mainly determined by the intensity and duration of irradiation of the light source. Researchers have found that UV irradiation with an intensity greater than 90 μW/cm2 for 30 min can effectively kill the SARS virus, and this is the effective dose against the SARS virus. Novel coronaviruses are also RNA viruses, and theoretically UV is effective in killing coronaviruses.

In practice, the deep UV inactivation dose to the novel coronavirus needs further experiments by relevant departments and institutions to clarify, and the current general reference is the inactivation dose against the SARS virus. Constrained by crystal quality, doping efficiency, and light extraction efficiency , the quantum efficiency and output optical power of UVC LEDs need to be improved . Under the same irradiation distance conditions, the UV irradiation intensity of UV LEDs is temporarily unable to reach the level of UV mercury lamps.

Therefore,  it is necessary to use longer time for UV LEDs and shorten the distance between the light source and the irradiated surface, so as to ensure an effective amount of disinfectant.

Besides the degree of freedom of output wavelength and the difference in output light power, UV LEDs and UV mercury lamps are also different in terms of volume, turn-on speed, power consumption, reliability, and safety. Compared with LEDs, UV mercury lamps are larger, have a long start-up time, cannot be used immediately, have high energy consumption, are fragile, and contain mercury, which poses a threat to the environment and human health.

With the formal implementation of the “Minamata Convention on Mercury”, it is a general trend that traditional mercury-containing light sources are replaced by cleaner and more efficient UV LED light sources. With the help of UV LEDs, technical application scenarios that cannot be achieved with traditional UV mercury lamps will also be realized. For example, UV disinfection technology based on UV LED light source can be combined with personal electronic product equipment to develop portable UV disinfection products.

3. Difficulty met in the development of UV LED

UV LED is still facing many challenges from the core material to the device process, UV LED performance improvement process facing the technical bottlenecks can refered on many article. With the technological progress, interdisciplinary, application integration, new applications continue to arise, the corresponding standards also need to be improved. Our existing UV standards and test means mainly around the traditional mercury lamp, the lack of applicability to UV LED, for example, UV mercury lamp germicidal wavelength mainly in 253.7 nm, and UVC LED best inactivation efficiency of the output wavelength is mainly distributed in 260 ~ 280 nm, which brings differences for the subsequent application of the solution.

Therefore, UVC LED light source urgently needs a series of standards from testing to application, to support the development of technology. Our relevant institutions have carried out the research of UV LED measurement, standard, testing, etc., and are gradually constructing the standardization system that matches the UVC LED application.

4. 222nm Far UVC led

The wavelength 222 led has successfully win the attention of peoples this year. It’s a new technology which can use in the crowd without harming human skin and eyes.

In April ,  a study in Japan showed that repeated irradiation of hairless mice with particularly sensitive skin using filtered 222 nm UVC light would not cause skin cancer or cataracts in them. It was thus proposed that deep UV radiation at 222 nm was not harmful to human skin and eyes.

Similarly, a related study conducted at Columbia University in the United States had shown that far UVC at 222 nm could not penetrate skin surfaces or eyes, was safe for humans, and could kill viruses.

There has been a lot of controversy in the industry regarding the sterilization effect and safety of 222 nm UVC light. Recently, Oxtail and Kobe University announced the research process and results of human testing.

According to reports, Oxtail and a research team from the Department of Plastic Surgery of Kobe University have completed a study showing that irradiating filtered 222nm UVC light on human skin can reduce the number of bacteria on skin without causing skin damage.

It is reported that the researcher used the Care222 device to irradiate the backs of 20 healthy volunteers ranging in age from 20-80 years old, and after 24 hours, all the volunteers did not show any signs of redness on their skin.

Then, to measure the flora counts on the skin, the researcher used a cotton swab to scrape the flora onto the skin on the back of the volunteer, and then irradiated again using the Care222 disinfection equipment. The colony counts were divided into three stages: before irradiation, 5 minutes after irradiation, and 30 minutes after irradiation. The final results showed that the Care222 disinfection equipment significantly reduced the number of flora by nearly 90%.

Three months after the irradiation, the researchers found that the volunteers’ skin test areas did not show any signs of erythema, and no adverse reactions were found.

Based on these test results, the researchers concluded that UVC at a wavelength of 222 nm is safe and antiseptic for human skin. The study has now been published in the journal PLOS ONE (Public Library of Science).

 

5. Conclusion

The UV LED industry related to UV disinfection and sterilization will be further developed. With the in-depth integration of production, education and research, the level of UV LED technology will surely be further rapidly improved, and UV disinfection technology based on UV LEDs will also be applied and promoted on a larger scale.

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