Here is a very basic run down on lighting.
normal output fluorescent - It's what you have now. They can be designated by bulb diameter as T5, T6, T8, T12, etc. If you lined the top of your 90 with about 8 of them, you would be able to keep some soft corals close to the top.
(power compact) - A step up from normal output fluorescent. You can keep soft corals and some lower light LPS
(Very High Output) - These bulbs are T-12 110w for a 48" bulb compared to 40w for the same size normal output bulb. You can keep soft corals, LPS
, and some lower light demanding SPS
(very high in the tank).
T5HO (High Output) - These are very popular because of their size, 5/8" diameter and high output (54w). Reflectors have been designed to make these bulbs very good. You can keep any type of coral using T5's, depending on the depth of the tank and placement of the corals.
(metal halide) - These are high intensity discharge bulbs. You can keep any type of coral. Many times, these are the best option for deep tanks.
Actinic bulbs are bulbs that put out light in the blue spectrum. 50/50 bulbs are 1/2 daylight spectrum and 1/2 actinic. Actinics are mostly just for your viewing pleasure as they bring out the colors in corals. Most of your saltwater bulbs do have blue in them and the actinics just supplement that.