Question about lighting a terrarium

[ChrisAZ]

Hello, I am a new member to this site looking for some guidance from some experienced members. I am in the process of building a glass terrarium measuring 45" tall by 30" wide by 20" deep. I am lining the walls with Epiweb and I am planning on lighting the enclosure with 2 ft. T5 fluorescent lights plus 1 or 2 small spotlights. My question is, would a 4 bulb T5 fixture be sufficient or should I order the 6 bulb fixture? Is there any sort of formula for lighting? I'm also looking for any experienced members with terrariums this size that would be willing to offer some guidance. I have a lot of questions. Thank you.