Jun 10
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Indoor Grow Lights
Today, the most widely used lights for professional indoor flower and vegetable growing are HPS/SON (high pressure sodium) and MH (metal halide). These are types of HID lights. Normal metal halide bulbs have a slightly bluish light and are used for the vegetative phase of growth, as their spectrum is close to sunlight and encourages normal to slightly leggy growth. Unlike high pressure sodium lamps, metal halide lamps also produce ultraviolet radiation, which may play a role in increasing the amount, quality, and potency of herbs or other materials produced by plants. High pressure sodium lamps may trigger a greater flowering response in plants and are thus used for the second (or reproductive) phase of growth. If high pressure sodium lamps are used for the vegetative phase, plants will usually grow slightly more quickly, but will also have longer internodes, and may be longer overall. Metal halide bulbs with added reddish spectrum as well as high pressure sodium bulbs with added bluish spectrum are also available for added flexibility for use with both vegetative and flowering growth.
Incandescent grow lights
Incandescent grow lights have a red-yellowish tone and low color temperature (approx. 2700 K). They are used to highlight indoor plant groupings and not as a true plant ‘growing’ light (although they may be labeled as such). Incandescent growing lamps have an average life span of 750 hours. In addition, they are less energy efficient than fluorescent or high-intensity discharge lamps, converting much of the electricity consumed into heat (rather than light).
Fluorescent grow lights
Today,fluorescents lights are available in any desired color temperature in the range from 2800 K to 6000 K. Standard fluorescents are usually used for growing vegatables (as leaf lettuce, spinach, and herbs) or for starting seedlings to get a jump start on spring plantings. Standard fluorescents produce twice as many lumens per watt of energy consumed as incandescents and have an average usable life span of up to 20,000 hours. This is 25 times as long as an incandescent. Cool white fluorescent lamps are sometimes used as grow lamps. These offer slightly lower performance, a white light, and lower purchase cost.
High Output fluorescents produce twice as much light as standard fluorescent lamps. A HO fluorescent fixture has a very thin profile, making it extremely useful in vertically limited areas. High Output fluorescents produce about 5,000 lumens per 54 watt bulb and are available in warm (3000 K) and cool (6500 K) versions. Usable life span for High Output fluorescent lamps is about 10,000 hours.
Compact fluorescents are smaller versions of fluorescent lamps and are used for propagation, as well as for growing larger plants. Compact fluorescents work in specially designed reflectors that efficiently direct light to plants, much like the HID lamps below. Compact fluorescent bulbs are also available in warm (3000K) and cool (6500K) versions. Usable life span for compact fluorescent grow lamps is about 10,000 hours.
High Output Fluorescent/HID hybrids combine cool burning with the penetration of high intensity discharge technology. The primary advantages to these fixtures is their blend of light colors and broad even coverage. In addition, electricity costs are substantially less than with incandescent lighting.
High-pressure sodium lamps
High pressure sodium lamps yield yellow lighting (2200K) and have a very poor color rendering index of 22. They are used for the second (or reproductive) phase of the growth. If high pressure sodium lamps are used for the vegetative phase, plants will usually grow slightly more quickly. The major drawback to growing under high pressure sodium alone is that the plants tend to be taller and leggier with a longer internodal length than plants grown under metal halide. . They are used in less color critical applications such as parking lots, street lights and for 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. Orange/red spectrum HPS is the spectrum plants use in their reproductive processes, which generally produces larger harvests of higher quality herbs, vegetables, fruits or flowers. Sometimes the plants grown under these lamps do not appear very healthy (although they usually are). This is due to the poor color rendering of high pressure sodium, which makes the plants look pale, washed out or nitrogen starved. Benefits to high pressure sodium lighting are their incredibly long usable bulb life (up to two years in many cases); and unparalleled efficiency at six times more light output per watt of energy consumed than a standard incandescent grow lamp. Due to their high efficiency and the fact that plants grown in greenhouses get all the blue light they need naturally, these lamps are the preferred supplemental greenhouse lights. But, in the higher latitudes, there are periods of the year where sunlight is scarce, and additional sources of light (aside from HPS illumination) are indicated for proper growth. It also ought to be noted that HPS lamps may cause distinctive infrared and optical signatures, which can attract insects or other species of pests; these may in turn threaten the various herbs, flowers, or vegetables being grown. High pressure sodium lamps emit a lot of heat which can cause leggier growth, this is typically controlled by using special air cooled bulb reflector/enclosures.
Combination HPS/MH lamps
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 is said by manufacturers to create an ideal spectral blend and extremely high outputs, but in reality it is a compromise on both situations. These types of lights usually cost quite a bit more than a standard light and have a shorter life span. Also because they use two smaller lights rather than one larger light the distance that the light penetrates is significantly shorter, in comparison to a regular hid bulb, due to the inverse square law of light.
Switchable, convertible & two-way lamps
Switchable, Two-Way and convertible lamps are used 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 used 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. To change between the lamps, only the bulb needs changing and a switch needs to be set to the appropriate setting. These are commonly known as conversion bulbs and usually a metal halide conversion bulb will be used in an HPS ballast since the MH conversion bulbs are more common.
LED grow lamps
Recent advancements in LEDs have allowed for the production of relatively cheap, bright, and long lasting grow lights that emit only the wavelengths of light corresponding to chlorophyll absorption peaks. These lights are attractive to indoor growers since they do not consume as much power, do not require ballasts, and produce a fraction of the heat of HID lamps. Since there is a significant reduction in heat, time can be extended between watering cycles because the plants transpire less under LED grow lights. A caution is warned to those growing with LEDs not to over water the plants.
There are four chlorophyll absorption peaks and LED grow lights use four different types of LEDs to hit all four peaks (two red and two blue).Early LED grow lamps used hundreds of 1 or 2 watt LEDs and were not effective replacements for HID lamps. Newer advanced LED grow lamps use automotive grade 6 watt LEDs and have shown similar results to HID lamps
Light Spectra
Different light spectra are used for the different stages of plant growth. The initial vegetative stage requires blue spectrum of light, whereas the later “flowering” stage is usually done with red–orange spectra. The lights can be bought by spectrum colour specifically, or some companies produce a full spectrum bulb which caters for all stages of growth.
The light is usually used in conjunction with a reflector, to control and intensify the light emissions, and will include an electrical ballast to control the current to the light. This is required because of the high intensity of the light that is necessary to produce something akin to sunlight.
