Well a LTA is going to keep his foot in the sandbed, so your lighting will need to reach the bottom of the tank. The one bulb that will almost always do this is metal halide. On a 55 gallone I would place 2 - 150's or 175's over the tank with supplimental VHO bulbs.
Another option would be to get a VHO retrofit kit of 440 watts. That should do it also. Everyones experience varies.
