A photobioreactor is a type of bioreactor that uses light as an energy source to facilitate the growth of photosynthetic organisms, such as algae or cyanobacteria. The reactor contains a light source, a growth medium, and a system to circulate the medium and deliver the light. The light encourages the growth of the photosynthetic organisms, which can then be used for a variety of applications, including biofuel production and wastewater treatment.