Ok.
Well the goal is to use as little wattage in the grow room as possible.
Im gonna add a 150w HPS to go with the 250w HPS, that along with ventilation will be slightly under 500W all together. (Grow-room is not finished yet)
All 4 walls will be isolated with a reflective material with ISO 3795. Everything, even the pots will be white so no light is lost.
Might add that the room is only 240x130cm "big"