Raising and lowering the light will change the PPFD the plant is getting hit with. When I get to mid flower I want 900 PPFD at the top and hope for 500 as far down as I can get it, by late flower I will bump it up to 600 at the lowest bud site and keep an eye out for light burn on the top, Above 1200 and it can get ugly fast if you dont have CO2. 

In the long run the DLI is what really matters though. I changed the hours the lights were on to 13/11 and held it at 45 DLI, I may go for 50 this time. 

BTW I am very new to LED's and I screw up a lot, so proceed with caution.