Generation of reactive oxygen species upon red light exposure of cyanobacteria from Roman hypogea

► Light is crucial for phototrophs but high light causes photoinhibition & radicals. ► Moderate red light reduces more biofilm activity than green & than white light do. ► Blue light triggers orange carotenoid protein related non-photochemical quenching. ► Moderate lights reduce cyanobacterial growth; dim lights promote photosynthesis. ► D-ALA produces radicals inside cyanobacterial cells shown by ESR spectroscopy.