Originally Posted by Seattle_Aquarist
Obviously you have two T12 bulbs over your tank. I am going to assume that you have about 2" of substrate and some sort of aluminum reflector behind the bulbs. If you have a 'standard 20H' (16.8" tall) I would estimate your PAR reading would be less than 30.......low light. If you have a 20XH (23.8" tall) I would estimate your PAR reading at less than 20.....low light.
What bulbs would I have to get to make it a high light? I know I would have to go to T5s but how many bulbs,watts.