Researchers have proposed a prediction that red-edge could be observed as on the Earth even on exoplanets around M-dwarfs. They pointed out that the first oxgenic photorophs are most likely to have evolved underwater to utilize visible light just like what had happened in the primordial ocean on the Earth. They examined light adaptation mechanisms of visible- and IR-radiation-using phototrophs required for adapting to land habitats and found out that IR-using phototrophs struggle to adapt to changing light condition at the boundary of water and land surface.