smoke24answered grow question 4 years ago 24hrs of light a day is really not good for the plants.....they need to rest just like we do. Humidity that low at any stage of growth is bad, being that low your Vapor Pressure Deficit is massive, basically the air is so dry its drawing moisture out of the leaves faster than the root system can compensate. You really want to be around 65% humidity at this stage of growth, and the sooner the better, because at 18% the plant will die. Best of luck and happy growing.