COMPACT FLUORESCENT AQUARIUM LIGHTING SYSTEM GENERAL INFO Compact fluorescent (aka power compact) aquarium lighting utilizes fluorescent bulbs that are bent in half. These VHO lamps deliver a higher concentration of light energy in a smaller space than straight tubes do, although the light concentration is less than with metal halides. They are also different from regular fluorescent tubes in that the four pins are at one end while other fluorescent lights have two pins on each end.
Compact Fluorescent LampsThere are two different incompatible standards for compact fluorescent lights, the straight pin style (aka European), and the square pin style (aka Japanese or Panasonic). The straight pin connector has the four pins in a straight row while the square pin connector has the pins in a square configuration.
Current USA fixtures use square pin lamps.
Coralife uses both square and straight pin lamps.
Neither standard is superior--you just have to be careful when buying replacement lamps that you get lamps with the correct pin configuration.