# Study on the Light Field Regulation of UVC-LED Disinfection for Cold Chain Transportation
## 2 Background  
There are several disinfection methods used in cold chain transportation, such as chemical disinfection, ozone disinfection, UV disinfection and so on. Chemical disinfection is often used to disinfect non-food goods in cold chain transportation. Its principle is to kill all microbial propagules and spores in the medium. Ozone disinfection and radiation disinfection are effective disinfection methods. [PERSON] et al. [5] employed an efficient cold atmospheric plasma (CAP) with argon feed gas to inactivate SARS-CoV-2 on various surfaces and achieved great results. [PERSON] et al. [6] applied surface discharge plasma treated air to deactivate the pseudo virus with the SARS-CoV-2S protein, which also provided a potential disinfection method. In contrast, the process of UV disinfection will not produce pungent odor and will not produce any chemical residues [7]; thus, it is an effective disinfection method in cold chain transportation. UV (ultraviolet) light in the band of 200-280 nm is UVC light, and UVC disinfection is a mature disinfection method. The principle is to use UVC light to destroy the DNA or RNA molecular structure in microorganism cells, thereby halting cell growth or regeneration and ultimately achieving the effect of disinfection [8]. [PERSON] et al. [9] examined the basic spectral properties of DUV-LEDs (Deep Ultraviolet) and the effects of UVC irradiation for inactivating foodborne pathogens, finding that the use of DUV-LEDs may compensate for the drawbacks of using LP-UV (low-pressure mercury UV) lamps to inactivate foodborne pathogens. [PERSON] et al. [10] examined the efficacy of UVC light prototype devices with the wavelengths of 275, 254, and 222 nm, and drew the conclusion that the UVC-LED (275 nm) exhibited superior SARS-CoV-2 disinfection activity compared to the mercury lamp (254 nm) and the excimer lamp (222 nm). [PERSON] [11] determined the susceptibility of SARS-CoV-2 to UVC light. As a result, a viral stock with a high infectious titer of \(5\times 10^{6}\) TCID\({}_{50}\)/mL was completely inactivated by UVC irradiation after 9 min, while the dose required for complete inactivation was 1048 mJ-cm\({}^{-2}\). [PERSON] [12] investigated the in vitro efficacy of 222-nm far-ultraviolet light (UVC) on the disinfection of SARS-CoV-2 surface contamination. They also investigated the titer of SARS-CoV-2 after UV irradiation (0.1 mW-cm\({}^{-2}\)) at 222 nm for 10-300 s using the 50% tissue culture infectious dose (TCID\({}_{50}\)). The results indicated that 222-nm UVC irradiation (0.1 mW-cm\({}^{-2}\) for 10 and 30 s) resulted in an 88.5 and 99.7% reduction of viable SARS-CoV-2 based on the TCID\({}_{50}\) assay, respectively. There are many other studies that indicate that UVC disinfection has great application prospects [13; 14; 15; 16]. There currently exist two main types of UVC light sources, the first of which is the traditional mercury lamp, which generates UVC light by breaking down mercury vapor discharge at high pressure. However, it has defects that include a complex structure, short life, and highly toxic elements. The second type of UVC light source is UVC-LED,which has gradually become a popular research topic [17; 18; 19]. Compared with traditional mercury lamps, UVC-LEDs have no highly toxic elements, are safe to use, will not pollute the environment, and are also characterized by a relatively single wavelength, targeted disinfection, a narrow spectral range, low power consumption, and small size [20; 21]. However, UVC-LEDs also have low light-output efficiency, poor reliability and high costs [20]. In the process of disinfection, the main disadvantage of UVC-LEDs is the uneven light field distribution [22; 23; 24; 25], which leads to excessive disinfection in some areas and incomplete disinfection in some areas. In addition, under the environment of cold chain transportation and the attenuation of UVC energy by an ice layer, traditional UVC-LED may not meet the disinfection requirements of cold chain transportation.