I have been away from RC for a while, I really like how this subject evolved. I agree with most of what was said. The only comment I would feel I need to throw into the mix is that the PAR reading is a useful tool but is not the whole picture. The comment that actinics do not do much more than make things look pretty in particularly suggest that the PAR value is the whole picture. Full spectrum light is important, and different corals and clams even of the same species will respond differently to different parts of the spectrum. They will also adapt to the intensity and spectrum they are kept under if it remains consistent. I doubt I will ever take a PAR reading. I observe the animals and make decisions as to whether to make changes in intensity or spectrum timing or position of animals in the tank based solely on observation of growth, color, behavior. I believe that the actinic lighting is a very important supplement for the broad spectrum daylight bulbs and is very beneficial for many corals, anemones and clams. The equipment would be expensive but the whole picture would be a plot of intensity vs wavelength at different depths combined with observations on growth, color and behavior. For a clam color and behavior are as important an observation on health as growth. - Mark