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Artificial Lighting

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:

  • Will this be a primary source of light for the plants, or as a supplement to natural light?
  • Where will the fixture be located? In a living area or basement “grow room”?
  • Is heat generation a problem or a plus?
  • How large of an area will be lighted?
  • How much “head room” (distance from plants to the light) do you want?
  • What is your budget for lighting? (Don’t get cheap here – light is a crucial parameter in orchid growing.) Consider purchase price, bulb replacement, and operating costs.

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 (MH)
10,000 hr life

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.

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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.

High Pressure Sodium (HPS)
20,000 hr life

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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 8ths of an inch – i.e., a T12 is 12/8ths or 1.5″ 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.

20,000 hr life

T5 fixtures are probably the best choice for lighting plants in a living area, and are excellent for isolated growing areas as well.

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2,000 hr life

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.

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Light Emitting Diodes (LED)
50,000+ hr life

LEDs 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 in excess of 100 lumens per watt.   There are entirely too many variations to discuss in the context of this article, so we’ll touch on some basics.

Monochrome LEDs each put out very specific wavelengths of light, so in early plant lights, colors need to be mixed in order to approximate the desired spectrum. You are probably familiar with the so-called “blurple” lights – a mix of blue and red LEDs. As the selected wavelengths of those chips matched the peak absorption areas of chlorophyll, they worked quite well and were used extensively by marijuana growers. Unfortunately, as orchid growers actually want to see their plants and flowers, so the lack of green in the spectrum produced an eerie, alien appearance, making those lamps unacceptable.  To overcome that, “white” LEDs are often used to make LED lighting more applicable to living areas.

So-called “white LEDs” are really ultraviolet or blue LEDs to which a coating of blended phosphors is added. The blue or UV wavelength excites the phosphors, which in turn emits light in a number of wavelengths that combine to appear as white light. Most “white” LEDs are manufactured with household lighting in mind, not plant growth. As the human eye is most sensitive to wavelengths in the green part of the spectrum, white LEDs often emit green very strongly, making them appear very bright to us, but may be quite lacking in the wavelengths plants need, especially toward the red end of the spectrum. As of this update, only a few “white LEDs” have had their phosphors tailored to meet plant needs while being acceptable to us, so it is common to find LED plant light fixtures use white in combination with various red LEDs – a combination that works very well.