Having had a 3' tall tank (2 of them intact), what you are thinking for nepenthes and in-fact for any plants IMO is very very low light. I used to use 4' - 4 tube T5HO + 4' 2 tube T8...but then I got greedy and upgraded it to a 8 tube T5ho. That was enough to get good light all the way to the bottom where my plants were located (10" from the bottom). I personally would try to look to 4' 4 tube T5HO fixtures at least. And I would recommend a daylight spectrum (sun blaster or philips or GE T5HO 6500K) with some extra for colour (I used a coral-life colormax). Intensity drops quickly so...that was one thing I learnt about tall tanks. Very very hard to get enough light to get "red" colour on plants at the bottom.