The level of available light is a crucial factor in the plant's health and appearance. Photosynthesis is the process where plants transform light energy into food energy. Like all living things, plants need food for energy. Plants use the energy of the sun to manufacture their own sugar, by the process of photosynthesis. Light energy, carbon dioxide, and water interact with the green plant pigment, chlorophyll, to produce plant sugars and oxygen, which is released into the atmosphere, supplying most of the oxygen on planet earth.
Phototropism is the natural inclination of plants to grow towards the light source.
Plants will actually bend toward the window and thus need to be rotated or have supplemental artificial light placed so that the plant receives even light. Otherwise, the plant will have excessive growth on one side and little growth on the opposing side. Photoperiodism is the plant's innate response to its environment. Even indoors, plants perform best in a rhythmic cycle of light and darkness that closely resembles their original habitat. Plants are absolutely dependent on light for their survival.