The tank is 48" x 36" x 12" and the lights are hung about 15" above the tank. The light covers the tank nicely without being much dimmer at the sides. I think that you could cover a 120G 48"x24"x24" with 2 of these lights hung over the tank 5" or so. These lights give a more normal look to the tank because the optics are not as narrow so it looks less "shadowy". You might have to see it in person to notice it.