Sunlight is considered as the ultimate source of energy. Plants are termed as autotrophic organisms as they require light for carrying out the photosynthesis process. The amount of light and intensity of light effect plant distribution, flowering and fruiting. Many species of small plants (herbs and shrubs) growing in forests are adapted to photosynthesise optimally under very low light conditions because they are constantly overshadowed by tall, canopied trees. Many plants are also dependent on sunlight to meet their photoperiodic requirement for flowering. The amount of light in aquatic habitats is responsible for the vertical distribution of plants in oceans.