Plants generally need four things to grow strong and healthy: carbon dioxide, water, nutrients and light. But plants grown indoors are seldom exposed to bright sunlight. If a plant cannot get enough sunlight at your window, you may have to use artificial lighting to get them to grow.
The sun emits very bright light that plants must often get used to. In winter when trees have lost their leaves, they may be subject to sun scald, a type of plant sunburn, if they have not grown used to the intensity of the sun. Because of this, many plants selected to become house plants are chosen for their low sunlight requirements, typically species that grow in the subcanopy of tropical rainforests. Species that grow under these conditions may be placed directly under an artificial light and will receive sufficient light to thrive. If a plant is not getting enough light, it will grow in such a way that it bends toward the sunlight.
Plants require sunlight to manufacture energy and grow. Light intensity affects this production of plant food, which in turn affects the plant's stem length, color and flowering behavior. Plants that do not receive enough supplemental lighting often become spindly and have weak growth. The plant's leaves may also be lighter green in color. An identical plant grown in sunlight will have more compact growth, stronger branches and larger, darker foliage.
Length of Exposure
Certain plants require varying periods of light exposure and darkness over the course of their life cycles. For example, a Christmas cactus flowers only after the days have become shorter and the plant receives less than 11 hours of sunlight. Plants grown under artificial light are often exposed to light for longer periods to enable the plant to manufacture sufficient food to survive. These plants should still receive no more than 16 hours of artificial light daily. Plants that receive more light than this will develop sun scald.
The color temperature of the light, or the wavelengths of light that each bulb produces, is another variable you need to consider in choosing a source of supplemental lighting. Light comes in a range of wavelengths, but plants utilize certain wavelengths only. If a plant receives lighting from a window, it receives the proper wavelengths of light. In this situation, an ordinary incandescent bulb is often sufficient for supplemental light. But if you plan to grow a plant in artificial light only, you should choose lighting specifically designed for growing plants. Green plants use light along the blue and red spectrum for photosynthesis and infrared light for flowering.