5.5K views · 231 reactions | When it comes to planted aquarium lights, many people want to know the PAR rating. PAR stands for "photosynthetic active radiation" and basically measures how bright a plant light is. However, many things can effect the PAR rating of a light — such as the distance from the light, height of the tank, use of an aquarium lid or not, and placement of the plants. #AquariumCoop | Aquarium Co-Op | Facebook