Well if you want to really get into it, then it depends on your strain. Purps and blue strains can handle lower temps. Lower temps usually makes your humidity higher. At least from my experience. If your strain of weed has a high mold resistance, then you could probably put it around 40, if it is less resistant to mold. It can be lower. I guess the exact range depends on the comfort level you have for your ladies. I was always more comfortable with high levels of humidity in veg. I kept mine at at least 70%, but that is me and that was vegging. When I put into flower, and start having buds form. I am lowering my humidity down to at least 45% lights on. Your humidity will most likely climb when lights are off. Mine as of right now gets up to 68% max lights off, and 50% least lights on. So when determining that range, you have to take into account the lights on and lights off factor.