Here in cloudy New England, conophytums generally want as much light as you can give them during the winter growing season. A sunny windowsill will suffice, but they do better in a nice open greenhouse. But be warned, plants can burn even here on a clear spring or summer afternoon, especially if their soil is very dry. In fact, I've probably killed more plants by frying them than by watering too much -- so be sure to provide some shade during the dormant period, and never move a plant into a brighter situation without slowly acclimating it to higher light levels.