Explanation:
Why do plants need light?
Light provides the energy plants need to make the food required for them to grow and flower. Plants are the only organisms able to use the energy from light to produce sugars, starches and other substances needed by them as well as by other living organisms.
(opens in new window)Is light color important to plants?
Certain colors or wavelengths of light are more important for plant growth than others. Leaves reflect and derive little energy from the yellow and green wavelengths of the visible spectrum. In contrast, the red and blue wavelengths of the light spectrum are the most important energy sources for plants.
Plants growing outdoors, in greenhouses or close to windows are exposed to a balance of wavelengths of light from the sun, including the blue and red light that plants need. In settings where plants receive little or no natural light, additional light from artificial sources must be provided for adequate plant growth.
(opens in new window)What types of artificial lights are available?
There are four primary sources of artificial light available for the enhancement of plant growth: incandescent; fluorescent; high-intensity, or gas, discharge; and light-emitting diodes.
As a single light source for plants, incandescent lights are not particularly good. They are a rich source of red light but a poor source of blue. Additionally, they produce too much heat for most plants and, if used, must be located some distance from the plants, thus reducing the intensity of the light the plants receive. Important from an economic point of view, incandescent sources are inefficient in converting electrical energy into light energy. Furthermore, a standard incandescent bulb's life is often only about 1,000 hours, whereas a fluorescent tube's life is normally 10,000 hours or more.
Fluorescent tubes provide one of the best artificial light sources available for plants in the home. They are about 2-1/2 times more efficient in converting electrical energy into light energy than are incandescent sources, making them less expensive to operate. Additionally, fluorescent tubes produce relatively little heat and are available in types that emit primarily red and blue light. As mentioned above, fluorescent tubes are relatively long-lived. They are also available in many sizes and shapes, though straight tubes in 2-, 4- or 8-foot lengths are used most frequently.
High-intensity, or gas, discharge (HID) lights, such as sodium-vapor or metal halide, are frequently used in greenhouses when supplementary light is needed. They are about 10 times more efficient in converting electrical energy into light energy than incandescent sources. Additionally, their bulbs are very long-lived. However, they emit a lot of heat and the fixtures needed to operate them are large, bulky and relatively expensive. These drawbacks, along with their lack of availability in small wattages, make them questionable for use in the home.
Light-emitting diodes (LEDs) represent the newest source of supplemental light for plants. They are extremely energy-efficient and very long-lived. LED lights can be customized to produce the wavelengths of light desired. For example, LED plant lights emit only the red and blue light needed by plants. They emit very little heat and require no ballasts or reflectors. Currently, however, the price of LED systems is high when compared with other sources.
(opens in new window)What light source is most popular for interior settings?
Given their modest initial purchase price, energy efficiency and ease-of-use, fluorescent lights are the choice of many indoor gardeners. Although cool-white fluorescent tubes remain the most popular choice, warm-white fluorescent tubes also seem fairly effective. Fluorescent tubes listed as white or daylight are less desirable for indoor plant growth. Cool-white tubes produce a small amount of red rays — in addition to orange, yellow-green and blue rays — but usually not enough for plants unless windows or other artificial lights provide additional red rays.
A few incandescent bulbs in the growing area can furnish needed red rays. A general ratio of incandescent to fluorescent light is about 3 to 10, so for every 100 watts of fluorescent light, you should provide about 30 watts of incandescent light for a better red-to-blue light balance.
The fluorescent tubes developed specifically for growing plants have a higher output
