Next, you need the light fixtures. For the 22gal tubs the 18in, 3light fixture from Lowe's is ideal. You need two fixtures one for each side of the box.
Both fixtures cost me $19.74 before tax.

The second picture is how the fixture should look before being mounted in the tub. Take off all the white pieces (have to unscrew the 'ground screw' to get the main body off). This will keep every ince of space maximized.