I forgot to mention that there is a chart the for a couple T8 fixtures so you can see how they compare. That post also has a guide to what is considered low, medium or high light. Just in case you didn't see the thread yet it's here: Lighting an Aquarium with PAR instead of Watts
Here's the chart from that post for T8 fixtures:
I can't believe they wouldn't give you a raincheck while you were there instead of making you come back. I usually tell them I can't make it back before the sale ends and never had a store not give me a raincheck that same visit. But at least they will give you one so that's good.