There are three different VL sources used in the study. White LED, which emits VL without UV domain, has achieved market dominance in applications due to its low energy use recently. In addition, FT and XE also emit VL only with the filters to block UV emission. The effect of the different VL sources was studied at pH8 under the same VL intensity, which was adjusted by changing the number of lamp and the distance from the light source to the sample flask. As shown in Fig. 1a, the inactivation of E. coli K-12 was much more efficient under FT than white LED and XE. Total inactivation of 7 log bacterial cells was achieved after 8 h irradiation by FT. There was an induction period, where the reactive species began to attack the bacterial cells but no serious damage leading to the inactivation of bacterial cell