Whoa! Leaf drop is more complex than inadequate light or too much water. Although either of those may lead to leaf loss on some plants, too much light, too little water, improper fertilizing, temperatures that are too high or too low, poor soil composition, and the addition of toxic substances to the soil or air can also cause leaf loss.

To answer Shawn's question properly we would need to have a lot more information starting with the name of the plant, the available light, watering frequency, repotting and fertilizing history, and temperature range.