Cyanobacteria, a type of bacteria that performs photosynthesis, utilize a photosensor to maximize their light-harvesting capacity under different light environments. A joint research team found a new photosensor that regulates yellow-green light-harvesting antenna in cyanobacteria. Further analysis of the cyanobacterial genomes revealed that this photosensor emerged about 2.1 billion years ago or more and evolved through genetic exchange between cyanobacteria.