That depends on the light and how hot it is. As close as you can get it, without burning the plant is good if it is a hot bulb. Go with organic fertilizers such as manure, guano, fish emulsion, compost, seaweed. Make sure that the fertilizer you are using is high in Nitrogen for the vegetation phase and high in Phosphorus and Potassium for the flowering phase. Also a good floir feeding spray mix is great as well, because it will give the plant a lot of trace elements and minerals that are not provided with regular fertilizers and plants can absorb nutrients from the leaves faster than they are absorbed and distributed from the roots.