I was thinking about converting a wooden cubby house in to a greenhouse type set up for my cacti. It is around 2.5 m by 1.8m and located in a sunny position. It has two windows, one at each end and I was also going to replace the roof iron with clear polycarbonate roofing sheets. Would this provide enough light for the cacti? Would I need more lighting from the side or would the above light be sufficient? Do cacti have preference for the direction of light?