Lighting the Aquarium Part 7: Photosynthetically Usable Radiation By Dana Riddle Photosynthetically Usable Radiation (PUR) is a portion of the spectrum that promotes photosynthesis. It is generally considered to be a subset of Photosynthetically Active Radiation (PAR, defined as that light between 400 and 700nm), but this is only partially correct as some Ultraviolet-A wavelengths, … Continue reading Lighting the Aquarium Part 7-Photosynthetically Usable Radiation