additional light added week 4 of flower.

Hi, this is my second grow. I have recently added another 600w full spectrum hps into my grow room. I have so far had a 600 and a 400 watt hps. 4 hydro 3 soil in the grow tent. I made a stupid decision of buying a 2 meter by 2 meter tent, the plants have actully grew really well and it's good to be able to have room to work although there is half the tent not being used. So I've decided to add a additional 600watt to fill in the gaps, it's going into week 5 soon and I just wondered if this will make much of a diffrence to yeild?, as some of the lower branches aren't getting enough. I've attached a picture so you can see how I've set it up. Everything is receiving a good source of light but weather it's going to improve yeild much is unsure.

Also thinking about just doing autos from now on to save electricity running 1800watts plus fans.