lighting question?

[Aquattro]

Originally Posted by phi delt reefer

a tank has a 48"x12" foot and is 18" deep would need two 250w halides which is 500w.

the same tank would need 4 48" t5 bulbs (54w a pop) - so thats 216w.

Well, a bit subjective here. The tank in question doesn't "need" 500w, only if you're using 250s. You could easily light the same tank with 2 x 70w, or 2 x 150w. Now this addresses light spread and coverage. What is in the tank may have different needs. I don't use T5s, but 4 x 54w seems low if I'm running an 18" clam tank. I would think that more than 4 tubes is "needed" . I could be mistaken, as I said, I don't use them, but "need" is a subjective term.
In comparison for cost, you need to compare costs of bulbs over time, costs of power, for MH, costs of cooling any heat generated. I know my chiller currently costs almost as much as running a second set of T5s