I'm pretty sure if you want to get the normal behavour out of your fish you need to have some light on the for the "appropriate" amout of time per day, to simulate daytime. But the need for lighting is in no small part the need to be able to actually see your fish.
By the sounds of the thread I was just reading (T8 vs T5) any type of lighting is suitable for plants. I have a Juwel Reckord 800 that has 2x 18w T8 lights and I have managed to keep plants happily growing in it. Increase/more intense lighting adds other complications like a greater need for nutrients and Co2.