If you want low tech why upgrade? I have the old halogen version of the fluval edge 6. I swapped out the bulbs for stock replacement LED's. I grow crypts, java fern, and anubius nana petite very well with this light and the tank is almost 100% algae free, but that is probably with some help from the cherry shrimp and couple nerites running around.
Just received my FugeRay 16" for my Fluval Spec V (5G). I think its perfect for low-light. Remove the legs and you will approach mid-light. It also makes the tank pop compared to the stock LED light assembly.
I think for any tank around this size, the FugeRay 16" is perfect. It's also clear that the Ray II 16" or 18" would be far too much for low-tech setup (unless all you're growing are mosses).