Usually, light intensity and duration are the limiting factors when maintaining plants indoors. The primary reason plants need light is photosynthesis. Photosynthesis is the conversion of light energy to chemical energy by plants. All life depends on this process. Plants need to photosynthesize to exist, and animals need plants for food as well as oxygen, which is a by-product of photosynthesis.
Light also affects plants in other ways.
Phototropism, the bending of plants toward light, will greatly affect plant form. Low-intensity light, with more red rays, will cause tall, spindly plants. Since light is often the limiting factor in indoor plant production, you should measure your light levels on a consistent basis. The light intensity at a location is determined by averaging readings taken at plant height on several days during both cloudy and sunny weather. Whether you are using sunlight, artificial lighting, or a combination of both, these meters will allow you to determine if your lighting is sufficient for optimum plant growth.