# Study on the Light Field Regulation of UVC-LED Disinfection for Cold Chain Transportation
## 4 Results
### Results of Experiments  
The experiments were conducted to investigate the effect of the disinfection of _E. coli_ through ice (30 mm) in two groups for different periods (5, 10, 20, 30, and 40 min). Each group after irradiation was put into the constant temperature incubator for 24 h at 37 \({}^{\circ}\)C. To avoid accidental errors, the experiment was conducted 3 times for each period, and the average value was taken as the result. Each Petri dish contained two square frames with side lengths of 50 and 20 mm, and the number of colonies in the two frames was counted to conduct the analysis of the results, the purpose of which was to compare the effect of uniform light on the disinfection effect. The final disinfection effect is shown in Figure 7a; the leftmost is the reference group, that is, the _E. coli_ after 0 min of irradiation. Group 1 is above, while Group 2 is below; from left to right are the results of different periods (5, 10, 20, 30, and 40 min) of irradiation in each group. The white dot in the figure is the _E. coli_ colony, the number of which is the indicator of disinfection effect. It can be seen that the number of _E. coli_ colony in both groups decreased rapidly. However, the speed of decreasing differed in two groups, including the speed of decreasing in inner frame and outer frame in the same group. Note the disinfection results of two groups after 30 min and 40 min, for example, as shown in Figure 7b. Firstly, in the comparison between up and down, the number of _E. coli_ colony in Group 1 was significantly less than that of Group 2 in the same period, and there were few _E. coli_ in Group 1 after 30 min, while there were still many in Group 2 after 40 min. Then, in the comparison of inner frame and outer frame in the same group, it can be seen that the decreasing speed is almost the same of inner frame and out frame in Group 1, while this differs a lot in Group 2. For quantitative comparison, the average results of each group are listed in Table 2.  
According to the parameters in the table, the disinfection rate (%) of each period can be obtained by the following formula:  
\[\alpha=\frac{N_{0}-N_{t}}{N_{0}} \tag{9}\]  
where \(\alpha\) is the disinfection rate, \(N_{0}\) is the number of _E. coli_ in the non-irradiation group (0 min), and \(N_{t}\) is the number of _E. coli_ after \(t\) minutes of irradiation. Then the disinfection rate of each group can be calculated, as shown in Table 3, and Figure 8 can be drawn according to Table 3 at the same time. Figure 7: **(a)** The disinfection results of two groups for different periods; **(b)** the detailed disinfection results of two groups after 30 and 40 min. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Times** & **Group 1 (in)** & **Group 1 (out)** & **Group 1 (Total)** & **Group 2 (in)** & **Group 2 (out)** & **Group 2 (Total)** \\ \hline
0 min & 254.00 & 937.00 & 1191.00 & 254.00 & 937.00 & 1191.00 \\
5 min & 203.33 & 764.67 & 968.00 & 215.33 & 859.00 & 1074.33 \\
10 min & 127.33 & 465.67 & 593 & 131.67 & 644.67 & 776.33 \\
20 min & 43.33 & 197.00 & 240.33 & 63.00 & 543.00 & 606.00 \\
30 min & 9.67 & 47.67 & 57.33 & 28.67 & 397.67 & 426.33 \\
40 min & 3.00 & 9.00 & 12.00 & 5.33 & 154.33 & 159.67 \\ \hline \end{tabular}
\end{table} 
Table 2: The disinfection results of each group (CFU/mL). Based on Figure 8, firstly, comparing the curve \"Inner of Group 1\" and \"Outer of Group 1\", it can be seen that the changes in the disinfection rates of the inner and the outer frames of Group 1 for different periods were almost the same, which proves the uniform effect of the designed system. Then, comparing the curve of \"Inner of Group 2\" and \"Outer of Group 2\", the disinfection rates of the inner and the outer frames of Group 2 differed greatly with time; this is due to the uneven UVC light energy between the inner frame and the outer frame of Group 2.