Light is composed of short and long wavelengths. Violet and blue wavelengths are the shortest, and oranges and reds are the longest. All of these waves are essential to photosynthesis, a chemical reaction used by plants to make food. Yellow and green waves are medium in length and do not contribute to photosynthesis. All wavelengths, however, combine to create the natural, white light required for uniform plant growth.
During their germination stage, young seedlings direct their energy toward leaf production. Foliage sustains a plant. Without foliage, there can be no photosynthesis, no food and ultimately no flower or fruit. At this stage, plants require blue light more than any other wave in the spectrum. Short, blue wavelengths encourage bushy growth. If seedlings appear "leggy" (have elongated stems), pale flesh or cannot support their own weight, then their natural light can be supplemented with artificial lights, such as fluorescent bulbs.
Plant leaves are green because they reflect green and yellow wavelengths. The waves within this color of the spectrum are not necessary for sustaining life.
Reproduction is the biological imperative for most living entities. Blue light assists the development of foliage, but, with the minor assistance of blue light, the long waves of red light allow a plant to flower and achieve maturity.
Plants thrive when exposed to six hours of natural, white light per day. Indoor plants rarely get this kind of exposure, especially during the darker, winter months. If plants appear leggy, if variegated leaves begin to lose their patterns or if plants are limp even after watering, then supplementing the plants' natural light conditions with artificial lights can be considered. Some gardeners use complex lighting stands. Depending on expectations, though, a simple fluorescent bulb can supply adequate light for most houseplants.
Experts from both the University of Missouri Extension and the University of Arizona Cooperative Extension agree that incandescent lights burn too hot to be beneficial supplemental light sources. These experts favor fluorescent lights. University of Arizona Cooperative Extension also states in "Arizona Master Gardener Manual" that specialized fluorescent grow lights do not "have any greater value than regular fluorescent lights." The experts from the University of Missouri Extension suggest providing a plant with 30 watts of incandescent light for every 100 watts of fluorescent light. This provides the plant with a balance of red and blue light waves.
Plants depend on the quantity of light (the amount of direct sunlight available to the plants), the quality of light (high amounts of red and blue wavelengths indicate high-quality light) and the duration of light. Duration refers to the amount of time plants are exposed to the light. More would seem to be better, but this is not the case. In order to flower properly, a plant must receive a certain amount of cyclical darkness. This is referred to as photo period or day length. Some plants, such as chrysanthemum, require at least 12 hours of darkness. Long-day plants, such as beets and radishes, require 12 or more hours of daylight. Day-neutral plants are able to mature properly under any light cycle.