Plants that are grown indoors often do not receive enough natural light to thrive. A plant that is weakened from lack of natural light will have weak, spindly growth. Indoor gardeners first began to light houseplants in order to supplement the natural light that they received from windows. Indoor gardeners eventually began to notice that plants grew better and flowered more under certain colors of light.
Plants are the only organisms on the planet that are able to convert light into foods such as sugars and starches. This process, which is known as photosynthesis, is why plants need light to thrive. White light is comprised of many different spectrums of light. Each spectrum has a different color. Plants are better able to absorb certain colors of this light than others. For example, plants do not absorb light in the green color spectrum well. Instead, this green color spectrum is reflected, which is why a plant's vegetation appears green. The two colors in the color spectrum that a plant absorbs best are red light and blue light.
All light bulbs are able to emit a certain amount of light from each part of the color spectrum. This is called the light bulb's color temperature. Tungsten light emits light from the red and yellow spectrum more than from the green and blue spectrum of light. White lights are very balanced in the light that they emit. Fluorescent lighting emits more light from the green spectrum of lighting. This is why certain lights will nourish a plant better than others.
Despite the fact that fluorescent tubes emit more green light, a plant will actually get more nourishment from the fluorescent bulb than from an incandescent light such as a tungsten light. This is because incandescent bulbs emit more heat, which requires them to be positioned farther away from a plant than a fluorescent bulb. As a bulb's distance from a plant increases, the amount of energy that the plant absorbs decreases. Most plants should be placed between 6 and 12 inches away from a light source in order to receive sufficient light to thrive. A fluorescent bulb that is designed to emit cool-white or warm-white will produce a significant amount of blue spectrum light, which will nourish a plant.
The duration of light that a plant receives can have an effect on blooming as well. Plants are often left under artificial light for up to 16 hours daily to compensate for the lower quality of artificial light and to provide adequate nourishment. Some flowering plants, such as poinsettias, need a certain amount of darkness in order to enter their flowering state. In order to force these plants into their flowering state you should reduce the light intensity to 10 hours daily or less until the point that they produce flowers.
Plant lights are often put on a timer in order to assure that the plant will receive consistent lighting. A light that is placed on a timer will always turn on and off at the same time. Because the timer will be used around plants with water, it should be the three-prong type so that it will be grounded.