I think 30" is too small, think about your container and how tall that is, then take away the actual height of the lights at the top, then factor in the distance you need between the light and the top of plants to make sure they don't get too hot. It is possible to grow in a 30" space forsure if you do various training techniques to keep your plants shorter, such as a SCROG style garden. I would really recommend a 6' tall space at least to grow at least fairly mature plants, and still have some space to move around.