A prokaryote that obtains energy from light is a Phototroph.
Phototropic bacteria or archaea are a group of prokaryotes which use the source of energy as light. These prokaryotes convert the light energy to chemical energy in the form of chemical bonds and have several photochemical mechanisms in their metabolic pathways. Depending on the metabolic pathway the bacteria follow, the phototropic prokaryotes use carbon sources and are autotrophs undergoing the process of photosynthesis.
The cyanobacteria are the most commonly known prokaryotes which are phototropic in nature.