Why shouldn't we turn on white light in the laminar airflow chamber immediately after UV treatment?

By fact UV sterillzation is based on the principle of mutation caused by UV C occurring in the DNA of several micro-organisms like bacteria,fungi and protozoa due to thymidine dimer formation(covalent bond formation in between two adjacent thymines in the same strand of the dsDNA which hinders biological processes like cellular DNA replication and transcription)between 245 to 300nm wavelength of UV. This mutation is reverted back by an enzyme called photolyase in the cell which starts working at 480nm(visible region of the spectrum). The phenomenon is called photo-reactivation. If the mutation is fixed then the cells may again start to replicate normally and cause contamination. Thus, it is a general procedure to switch off UV and leave the LFC in dark for at least 15 minutes before turning the white lights on.