What Is PAR?
PAR (Photosynthetically Active Radiation) measures the amount of usable light — specifically the wavelengths plants and photosynthetic corals can actually use — reaching a given point in the tank, rather than just how bright a light looks to the human eye. It’s measured in micromoles per square meter per second (µmol/m²/s) with a PAR meter.
Why PAR Matters More Than Wattage
Two lights can look equally bright but deliver very different PAR at the same depth, which is why matching a light to livestock by wattage alone is unreliable. Low-light plants and soft corals generally need modest PAR, while SPS corals and high-light planted setups need substantially more — running PAR too low stalls growth, while running it too high can bleach corals or trigger algae blooms in a planted tank. PAR also drops significantly with water depth, so the same fixture delivers less usable light to the substrate in a deep tank than a shallow one.
Shop Aquarium Lighting
See Marine Aquarium Lights for reef fixtures or Planted Aquarium Lights for freshwater planted setups.
