ive made a new grow box as of today lol. it measures at 18.1/2" by 17 1/2" and its 30" tall. would i need the 140mm for this or should i still use the 120mm? this box will be for auto strains and will be using just red spectrum in it. plannin on puttin a 200w ontop and 3 45w around the plants. thanks for the advice