Neps like ampullaria, bicalcarata, etc. are called "lowlight" by so many authors but they should clarify what they mean by saying that these species will TOLERATE lowlight, not that they actually GROW BETTER in lowlight conditions. They will grow bigger pitchers, grow faster and be healthier overall in brighter light especially if you are growing with artificial light.
The main problem with bright sun light is that bright sun evaporates humidity quickly and will burn plants, in a terrarium you can make things super bright but since the light source (bulbs) is seperated from the plants the humidity (if sealed in)remains far higher and you get the benefit of both extreme humidity and bright lighting (= quicker growth). My N. bicalcarata grows directly below a 400 watt metal halide and loves it (I got it as a 12" diameter plant in June of 2002), it is now 54" across and making 7" tall/round pitchers. My amps. (2 pure green variety) are directly under the 6 40 watt tubes they have 8" leaves with 2 1/2" tall pitchers and a main vine of 10" tall and they already have several basal shoots around the main stem with small pitchers.
Do not be afraid to give your plants a little suntan by increasing the light, as long as the humidity is high they will adapt within a few leaves (i.e. months) and reward you more for all your efforts. This may mean slightly shorter and thicker leaves but bigger pitchers that last longer, depending upon the species of course. I was so careful with N. northiana giving it low light but I eventually moved it to the brightest lowland tank and it has grown far better/faster is now pitchering and is making 3" leaves and 3" pitchers that turn a awesome yellow with red speckles and slightly flaring striped peristome. Don't buy the lowlight hype, give 'em lotsa light (and humidity)!