extremely noob question

what do you call the casing thing that surrounds t5 lights? like in this picture? and any other information on aquarium lighting because all this is so confusing to me!!!ush: please help this noob http://i672.photobucket.com/albums/vv90/cheddar254/image001.png

 

Generally they would be called pendants, but obviously that one doesn't hang, it clips on the side of the tank. I'd just call it a lighting unit hey...
Housed somewhere in there would be ballasts to start up and supply power to the T5's.