I use a rather strong LED grow light that I had from seed starting and plant grow out. I only use it as that's what I had on hand. Probably overkill, but works fine. I think I'm currently doing 16 hours on.
I've had great success with many different types of lights on the Phyto. I've used:
Old Desk lamp with "Curly Q" florescent bulb - worked great but produced more heat that I like.
Plant Grow LED (t5's) - Worked great but too much light spill for this application (they were 48" long).
Literally a desk lamp with incandescent bulb -
LED Grow Lights (current setup) - Has worked great but I need something smaller and less "sprawling" so I can better control the light and only light my Phyto.
LED Flexible Strip Lights (due to arrive next week) - I'll be wrapping these around the actual Phyto container so the light is more direct and more where I want it rather than all over the room.