i go to 18"
A t-12 set up is cheap and works.
I have this set up I use from time to time.
My set up is (4) 24" T-12's 20 watts each at 6500k it's a light blanket.
I also have some 2600ish k's (don't use but may add to my hps room for some side lights).
These thing may be old school but...