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Plant Grow Light Options
Most incandescent plant lights are best used to highlight indoor plant groupings and have very little use as a true plant 'growing' light, even those that are labeled as a "grow light". Newer color corrected incandescent spot grow bulbs are suitable for adding supplemental light or highlighting to a single plant, such as an orchid or indoor bonsai tree.
On a cautionary note, you should never place an incandescent bulb closer than 24 inches above your plants. Incandescents burn very hot and will burn plants when placed close enough for them to appreciably affect plant growth. Most incandescent bulbs have a relatively short average life span of 750 hours.
Fluorescent Plant Grow Lights
Recent advances in fluorescent technologies provide the indoor gardener with a multitude of options. Not only can you start your seeds with fluorescent lighting, with new high-output and compact fluorescent technology, you can grow full size plants that produce full-sized fruit and flowers.
Standard Fluorescents (T-12 & T-8) are still an excellent choice for starting seedlings to get a jump start on spring plantings. They also are excellent for cultivating a cool weather harvest of leafy greens in the basement year round. Leaf lettuce, spinach, and herbs all will do well year round under fluorescent lamps.
The trick to using them successfully is to keep standard fluorescent bulbs no further than 4 inches away from the tops of the plants. Since the tubes burn relatively cool to the touch, you do not have to worry about burning plants unless they are actually touching the bulb. Fluorescent tubes are an excellent choice for the display and grow lighting of African violets, small cacti and succulents, and many kitchen herbs. New advances in color blending make full-spectrum standard fluorescent tubes one of the truest color rendering lamps on the market today. Standard fluorescent tubes are more efficient than incandescent bulbs, producing twice as many lumens per watt of energy consumed with an extremely economical usable life span of up to 20,000 hours... more than 25 times as long as an incandescent.
High Output T5 Fluorescents produce almost twice as much light as standard fluorescents while still burning very cool to the touch. HO fluorescent fixtures have a very thin profile, around 3 inches in most cases, making them extremely useful in vertically limited areas. Most can be hung vertically on a wall for side lighting as well. High Output T5 Fluorescents produce about 5,000 lumens per 54 watt, 48-inch bulb and are available in warm (3000K) or cool (5000-6500K) versions. Average usable life span for High Output Fluorescent tubes is about 10,000 hours.
Like standard fluorescent fixtures, High Output fluorescent fixtures are available in both two and four-foot lengths. Unlike standard fluorescent fixtures, High Output fixtures are available in 2, 4, 6, and 8 tube models.
An eight-tube four-foot High Output fluorescent fixture produces as much light as a 400 watt metal halide lamp (40,000 initial lumens), but spreads that light much more evenly over the growing area. Most High Output fluorescent fixtures can be hung vertically against a wall for very effective side lighting applications.
Compact Fluorescents take the cool burning fluorescent technology and pack it into a focused, high output "bulb", that you can use not only for propagation, but for growing larger plants as well. Compact fluorescents work in specially designed reflectors that efficiently direct light to the plants, much like the high intensity discharge lamps described below.
Compact fluorescent bulbs are also available in warm (3000K) or cool (6500K) versions. Average usable life span for Compact Fluorescent bulbs is about 10,000 hours.
High-Intensity Discharge (HID) Plant Grow Lights
High Intensity Discharge (HID) Plant Grow Lights High Intensity Discharge (HID) lamps in metal halide (MH) and high pressure sodium (HPS) have shown themselves to be particularly suited for growing large plants indoors. Initially these lamps were utilized for horticultural purposes as supplemental greenhouse lighting, allowing commercial growers to add lighting to their crops on cloudy days or extend the day length during the winter months.
Full size HID plant growing lights are comprised of a remote ballast, a reflector for directing light down to the plants, and a lamp cord that connects the ballast to the reflector and incorporates the mogul socket that holds the bulb. Historically, HID lamps were constructed with a classic magnetic core and coil transformer, but now new electronic versions are commercially available that allow dimmability, weigh much less than standard ballasts, as well as offering other advantages.
Metal Halide (MH) is a highly efficient light source capable of delivering a white light in the range of 2700 to 5500 Kelvin degrees with a typical Color Rendering Index (CRI) ratings in the mid-60's to mid-70's. Some lamp chemistries even obtain CRI's in the 80s. The CRI is an index that measures how closely an artificial light source matches the natural colors of sunlight, with 100 being a perfect score. In contrast, high pressure sodium lamps (below) yield yellow lighting (2200K) and have a very poor color rendering index of 22. By varying the blend of chemicals in the arc tube, metal halide engineers are able to alter the characteristics of the light output. This flexibility in design is what makes metal halides so versatile. White light is a very important attribute of metal halide technology, because it is the closest to the natural sunlight that people prefer.
Metal halide lamps are widely used where color rendering is important such as stadiums, malls, manufacturing plants, and supermarkets. For horticultural purposes, metal halides tend to produce a shorter, more compact plant habit that more closely resembles plants grown outdoors. A plants appearance growing under most metal halide lamps is almost identical to those growing outside, which makes it the preferred lamp for use in living areas. Horticultural metal halide lamps have an enhanced red spectrum, hardly noticeable to the naked eye, which is added for improved fruiting and flowering without sacrificing plant appearance. Metal halide lamps are about five times more efficient than their incandescent counterparts and last up to 25 times longer, with a usable lifespan between 10,000 and 20,000 hours, depending on the wattage.
High Pressure Sodium (HPS) lamps have been used for years in less color critical applications such as parking lots, street lights and as supplemental greenhouse lighting. The benefit of high pressure sodium lamps to the horticultural industry is their ability to enhance the fruiting and flowering process in plants. The orange/red spectrum HPS produces is the spectrum plants use in their reproductive processes, which generally produces larger harvests of higher quality fruits or flowers.
The major consideration to growing under high pressure sodium alone is that the plants tend to be taller and leggier with a longer internodal length (spacing between branches) than plants grown under the bluer light of metal halide. Another factor to consider is that plants generally do not appear very healthy growing under HP Sodium light. The operative word being 'appear', because in fact most plants do grow very well under HPS lighting. As a result of the poor color rendering characteristics of high pressure sodium, the plants tend to look pale, washed out or nitrogen starved.
The benefits of high pressure sodium lighting include an incredibly long usable bulb life... up to two years in most cases; and unparalleled efficiency at six times more light output per watt of energy consumed than a standard incandescent bulb. Due to their high efficiency and the fact that plants grown in greenhouses get all the blue light they need naturally from the sun, HP Sodium lamps are the preferred supplemental greenhouse light. Many indoor gardeners will grow their crop under metal halide lamps to keep the plants more compact during vegetative growth and then switch to a high pressure sodium system for the fruiting and flowering stage to increase yields and fruit quality.
Combination HPS/MH lamps combine a metal halide bulb and a high pressure sodium bulb in the same reflector, either with a single integrated ballast assembly or two separate ballast assemblies. The combination of blue metal halide light and red high pressure sodium light creates an ideal spectral blend and extremely high outputs.
Convertible, Switchable & Two-Way lamps are configured to burn either a metal halide bulb or an equivalent wattage high pressure sodium bulb in the same fixture, but not at the same time. These fixtures are ideal for propagating and vegetatively growing plants under the metal halide, then switching to a high pressure sodium bulb for the fruiting or flowering stage of plant growth. Generally, all that is required to change between one and the other is to change the bulb and set a switch to the appropriate setting.
Light Emitting Diode (LED) Grow Lights
Plant lights that utilize Light Emitting Diodes (LED) are now hitting the market after a decade of research by universities and NASA. LED Plant Grow Lights for hobby use are still in the early developmental stages, however the potential benefits of this new type of plant light include their extremely low power consumption, low heat production, extremely long lamp life, and their ability to refine the spectrum of light emitted to only those that the plant actually uses for photosynthesis. And while the future holds great promise for LED plant lighting, present drawbacks for home or hobby use include poor color rendering, a comparatively high initial cost, and limited depth penetration.
Safety & Resources
It is of utmost importance when purchasing plant growing lamps that every consideration to safety be observed, since growing lights are electrical devices that in many cases are in close proximity to water. Many companies claim their lighting systems are fully Underwriters Laboratories (UL) listed and approved for use in damp locations, when in fact, only their components have been independently certified.
Underwriters Laboratories (UL) thoroughly tests many indoor lighting systems for safety. A UL Listing for a lighting system is only valid when the entire manufactured system is submitted for testing and safety approvals and is sold as a complete light system.
Beware of no-brand and do-it-yourself lighting kits. Paying a few dollars more for a system that meets the high standards of safety set by Underwriters Laboratories could save that amount many times over should a shoddily manufactured lighting system cause a fire in your house.
You can find a large variety of safe, UL and CUL Listed indoor grow light systems at most reputable Earth-Friendly, Water-Wise Garden Supply Retailers in the U.S. and Canada.