Have you ever considered growing vegetables under lights during winter? It’s an excellent way to extend your current growing season or to get an early start on next spring. But before you decide to invest in creating a winter growing system under lights, some basic information about plants and light will help.
Plants depend on light in several ways. Best known is for photosynthesis, in which the energy contained in various wavelengths of light is captured by the pigment chlorophyll and used to drive the chemical process that produces glucose to feed the plant. Because red light and blue light are most efficiently absorbed by chlorophyll in a leaf’s upper layer, it was long thought that green light was largely reflected from leaves, giving them their green color. But it’s now known that a sizable amount of green light passes into a leaf and travels deeper into its structure than red or blue light does, where it too is absorbed by chlorophyll. Green light is also better able to pass beyond the uppermost leaves of a plant, reaching the lower ones as well. In these ways, green light too plays an important role in photosynthesis. However, plants depend on light not only for photosynthesis but also to regulate their development via photoreceptors that trigger various reactions when struck by particular wavelengths of light. Blue light triggers reactions that help produce strong roots and vigorous leaf growth, which makes it particularly influential during the early stages of plant development. Adequate blue light, for instance, ensures that young plants grow compact and bushy, not leggy. Red light, on the other hand, triggers reactions that stimulates stem elongation as well as flower and fruit production, so it’s especially important later in the plant’s development. And while it plays only a relatively minor role in plant function, yellow light may be involved in helping plants manage environmental stresses, such as drought.
One decision involved in creating a setup for growing plants indoors is what wavelengths of light to provide. If your plants have no access at all to natural sunlight, like mine which are grown in my basement, then you need to use full-spectrum grow lights. These produce wavelengths across the spectrum from blue to red, essentially mimicking the proportions of these wavelengths contained in natural sunlight. At the same time, they usually provide very small amounts of UV and far-red light as well, both of which, in limited quantities, also have benefits for plants. So with full-spectrum grow lights, your plants will be getting all the light wavelengths they need. Of course, more experienced indoor gardeners may want to supplement full-spectrum lights with more blue or red light either during particular stages of their plants’ development or depending upon the needs of the particular species of plants that they’re growing. But for the average indoor gardener, especially the beginner, using full-spectrum grow lights greatly simplifies their lighting choices.
However, decisions regarding indoor plant-growing don’t end here because different kinds of grow lights produce light in different ways, again creating choices as to which lights to buy. One option is fluorescent lighting. Many beginners choose these because they can often be purchased at an economical cost. Fluorescents frequently tend toward emitting a somewhat larger proportion of blue light and are therefore most helpful in getting young plants to grow well. I’ve found that young leafy greens (cabbage, kale, lettuce, etc.) do extremely well under fluorescent lights, although less so as they mature. Bear in mind, too, that fluorescent lights produce a generally mild heat when operating. So if you want some extra warmth for germinating seeds or encouraging new seedlings, fluorescents can provide it. When buying full-spectrum fluorescent lights, look for the label full-spectrum T-5.
Alternatively, LED strip lights are a very popular choice among indoor plant growers. Because they’re extremely efficient in using electricity, they have low operating costs. They’re also widely available in a range of options in addition to full-spectrum. You can buy targeted-spectrum LEDs that have a greater proportion of either blue light or red light than a full-spectrum LED has, enabling you to switch out the lighting to suit your plants’ stage of growth. There are also adjustable-spectrum LEDs by which the same strip of lights can be made to emit different proportions of blue or red depending on your plants’ current needs. Of course, the more elaborate or sophisticated an LED grow-light setup is, the greater the initial cost will be.
A third type of grow light consists of High-Intensity Discharge (HID) ones. These are typically less expensive to purchase than LED grow lights, but being much less efficient, they’re significantly more costly to run. There are two kinds of HID grow lights depending on the gas they employ – High Pressure Sodium (HPS) lights, which tend toward the red end of the spectrum, and Metal Halide (MH) lights, which tend toward the blue end. Note that all HID lights generate a large amount of heat, requiring very plentiful ventilation.
How close to your plants grow lights should be placed depends on the type of lights being used. Because of their very substantial heat, HID lights need to be several feet above the plants to avoid burning them. For my 40-watt fluorescent bulbs, in contrast, I’ve found that 4 to 6 inches above the plants works extremely well. And because they operate much cooler than fluorescents, LEDs can be as close as 2 inches above the plants. Also, regardless of distance from the plants, make sure that the lights you use are water-resistant because in watering your plants there will inevitably be splashes. Fortunately, most lights made specifically for growing plants are not only splash-proof but also designed to tolerate a very humid environment as well.