That wouldn't necessarily be the outcome of adding another light. It all depends on the type of light source, depth the reading is being taken at, reflector or lens type in the fixture, how far apart from each other they are placed. There will be an increase in PAR yes but it wouldn't always double. If you look at the BRS videos where they test the AI Prime HD or the RedSea LED90 you can get a good idea of what happens to the PAR and coverage when you start adding additional lights.