LIGHTAll of us know that the sun is the ultimate source of energy for all activities in our biosphere. The electromagnetic radiations from the sun supply energy which warms up the earth and the atmosphere to provide a favourable global temperature for the living organisms. In addition. light plays a variety of roles in the living world. It is essential for photosynthesis, the process by which light is converted into usable chemical energy. It is involved in the transmission of information, for instance, it helps plants and animals to programme their life cycles. coordinates the opening of buds and flowers, dropping of leaves and a variety of other physiological processes. Variation in theamount of light generally affects the local distribution of plants. In animals light regulates reproduction, hibernation and migration and of course makes vision possible. All these biological phenomena are readily influenced by variation in the intensity, and by seasonal or diurnal variations of light.