on an 8 gallon pretty much any PC light is medium intensity..
the length of the bulb isn't as important as the wattage is.. a 9'' bulb im going to very vaugely guess is a 12 watt bulb.. 2 of these, one 10000K and one actinic would be a perfect combo for most LPS and soft corals..
just one bulb i would really limit to simply softs.. mushroom, xenia, zoos, etc..