12-14 hours seems a bit much
the guide(s) I read suggest 10-12 hours, same as the sun.
I remember there were time when I position 2 CFL too close, the middle area start turning yellow too. irrc light can destroy chlorophyll.
Are those HC on the side grow better? When the parameters are right AND root settle, their leaves are 2x larger. (around from 1mm to 2mm)