It's a 20 high, sorry I should have clarified.
No problem . Here's the one you'd want for the high http://www.aquatraders.com/24-inch-4x24W-T5-Aquarium-Light-Digi-Timer-Fixture-p/52323.htm
Or
http://www.aquatraders.com/24-inch-4x24W-T5-Aquarium-Light-Fixture-p/52303.htm
If you don't want the timer