For those not lucky enough to have a greenhouse, or who have run out of space on window sills, the use of artificial light is a major "plus" to growing
You have a lot of options when it comes to choosing lighting, but you should do some thinking and planning before making a purchase. For example, some things to consider include:
There are four basic types of lighting available - High Intensity Discharge (HID), fluorescent, incandescent, and light emitting diodes (LED) - each having its own pluses and minuses.
High Intensity Discharge (HID)
HID lighting is the most energy-efficient way to provide light in terms of light output per watt consumed, and there are two types of HID lights commonly used - Metal Halide (MH) and High Pressure Sodium (HPS). Sometimes growers will use a combination of both.
They are very bright, and do generate a great deal of heat, so may not be the best choice for living areas of your home.
Metal halide bulbs produces light that favors the blue part of the spectrum, which is excellent for plant growth. If you are seeking a HID light for your primary light source, metal halide is the way to go, especially when you consider that newer technology has led to bulbs having boosted levels of the red end of the spectrum.
High Pressure Sodium (HPS)
High pressure sodium bulbs emit light in the orange-red part of the spectrum, which can induce budding and flowering in plants. For that reason - and because they can lead to "leggy" growth - HPS bulbs are better suited as supplemental light sources, and are often used in greenhouses. The output spectrum tends to override the colors of flowers when viewed or photographed. They are more economical to use than MH, due to the greater light output and longer bulb life. They are often used in conjunction with metal halide bulbs.
20,000 hr life
For years, folks using fluorescent lighting have typically used inexpensive "shop lights" that utilized 4-, 40W T12 bulbs. Those bulbs typically had output levels in the neighborhood of 35-40 lumens/watt, and typically had to be "right on top of" plants in order to provide adequate light levels. Fortunately, technology has advanced to the point of giving us highly efficient, long life compact fluorescents (CFL) and smaller diameter, more efficient T5 tubes. (Incidentally, the "T" number designation indicates the nominal diameter in 12ths of an inch - i.e., a T12 is 12/12ths or 1" in diameter.) Because they generate so little heat, it is possible to place the lights quite close to plants without fear of burning them. Like HPS and MH bulbs, one can find fluorescents that favor the red end of the usable spectrum (those with a "color temperature" of 2700°K to 3000°K) or blue end (greater than 7500°K), but those in the 5000°K to 6500°K range tend to be sufficiently "broad spectrum" to be a primary light source.
T5 fixtures are probably the best choice for lighting plants in a living area, and are excellent for isolated growing areas as well.
The old standard incandescent lamps may be the least expensive to purchase, but they inefficient and put out a poor spectrum of light for plants. You'll note that they are often tinted blue to shift the spectrum away from their strongly red output. If you suddenly need to supplement the light on a single plant, you might get by with an incandescent grow light, but you'll actually do much better with another choice.
Light Emitting Diodes (LED)
LED's are the latest in the evolution of horticultural lighting. They produce the least amount of heat, and as the technology advances, it is possible to get as much as 100 lumens per watt from them. At this stage of the game, however, the cost is quite high for modest-wattage units, and as the LED's put out very specific wavelengths of light, colors need to be mixed in order to approximate the sun's spectrum. So far, the color rendition of LED's is not up to par.
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