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| Detailed Information on Grow Lighting |
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Detailed Information on Grow Lighting
Lighting is one of the five major factors to consider when creating a support system for your plant life, (water, nutrients, oxygen and CO2 are the others). Thus if you plan to grow inside, out of season, you must supplement the sunlight normally required for proper growth. This can be done with three different kinds of lighting, incandescent, fluorescent, and H.I.D. (High Intensity Discharge). These are the most popular types of lighting for gardening purposes. There are many other kinds of lighting, but they don't produce proper color (kelvins) that is suitable for growing.
Incandescent lighting- These are the least efficient and least effective method of lighting, for plant growth. Incandescent lighting is the same as what is used in the average medium base household fixtures. This type of lighting is a very poor choice of lighting for your garden because of their inefficiency.
Fluorescent lights- These are a little better choice than incandescent lights due to the fact that they are about twice as efficient (lumens of light output per watt of electricity used). However these lights are not very effective in comparison to an HID (High Intensity Discharge) system and these lights must be less than 12 inches away from their subjects to ensure successful growth. However, some find that our T-5 fluorescent lights are perfect for use with seedlings and cuttings as well as for use with other plants that do not require the high intensity of H.I.D. (High Intensity Discharge) lighting.
H.I.D. (High Intensity Discharge)- These lights are by far the most efficient and effective lights being used by growers today. There are two types of H.I.D. (High Intensity Discharge) lamps that have suitable light spectrums (color range) and intensity for plant growth. MH (Metal Halide) lamps are rich in the blue light spectrum, similar to full summer sun. HPS (High Pressure Sodium) lamps are rich in the red/yellow spectrums, similar to the color of the fall sun.
METAL HALIDE
(MH)
MH (Metal Halide) bulbs are very efficient and produce between 70 and 115 lumens of light output per watt of electricity used. MH (Metal Halide) bulbs produce a light that is very close to full summer sun, with a spectrum rich in the blue end. This promotes fast vegetative growth and compact, stocky plants with short internodal leaf spacing.
MH (Metal Halide) bulbs create light by passing electricity through an clear inner arc tube that is enclosed in the vacuum of an outer clear glass tube. This inner arc tube contains mercury and other metals in iodide form. When electricity is applied to these metal iodides they give off very intense light and heat. The outer casing can also be phosphorus coated. Most gardeners prefer the clear bulb, as it produces the brightest white light available.
MH (Metal Halide) bulbs come in sizes from 70 to 1500 watts with the 250 w, 400 w and the 1000 w being the most popular sizes for gardening. All MH (Metal Halide) bulbs need to run with a ballast (a ballast is a transformer that steps up the voltage to the proper amount needed to ignite the iodides), that is designed to run that specific bulb size.
The bulbs themselves need to be burned in a specific position. They come in three types: Vertical (marked BU or BD), Horizontal (marked HOR) and Universal (marked U). The universal bulbs can be burned in any position, but they still are more efficient when burned vertically.
MH (Medal Halide) bulbs should be replaced about every 10,000 hours of use or approximately 18 months (as per an 18 hour / day on cycle).
HIGH PRESSURE SODIUM
HPS (High Pressure Sodium) bulbs are the most efficient bulbs that are available for grow lights. They are high in the red and yellow parts of the light spectrum and low in the blue, this imitates the fall sun. Because of this spectrum some plants that are grown with HPS (High Pressure Sodium) lights will grow elongated and rather leggy, while many other plants are not affected by the limited light spectrum. For plants that normally bud and flower in the fall an HPS (High Pressure Sodium) is usually the light of choice because it's light spectrum promotes flower production.
There are color corrected HPS (High Pressure Sodium) bulbs (such as the Son Agro) available for improved growing with HPS (High Pressure Sodium) efficiency. These are designed specifically for indoor horticulture, and have a more balanced color spectrum.
HPS (High Pressure Sodium) bulbs are made out of a translucent ceramic arc tube containing a mixture of sodium, mercury and xenon gas. This arc tube is suspended in an outer glass shield (bulb). HPS (High Pressure Sodium) bulbs range in power from 35w to 1000w, with the 250w, 400w, 600w and 1000w being the most popular for horticulture use.
HPS (High Pressure Sodium) bulbs should be changed no later than 24 months from initial use. These bulbs (like the Metal Halides) also slowly lose their brightness over time, so to maintain proper light intensity the bulbs must be changed at the end of their rated life.
Selecting a Grow Light
Plants have the unique ability to manufacture their own food. The food manufacturing process is called photosynthesis. Photosynthesis is carried out by many different organisms, ranging from plants to bacteria (Figure 1). The best known form of photosynthesis is the one carried out by higher plants and algae, as well as by cyanobacteria and their relatives, which are responsible for a major part of photosynthesis in oceans. All these organisms convert CO2 (carbon dioxide) to organic material by reducing this gas to carbohydrates in a rather complex set of reactions. Electrons for this reduction reaction ultimately come from water, which is then converted to oxygen and protons. Energy for this process is provided by light, which is absorbed by pigments (primarily chlorophylls and carotenoids). Chlorophylls absorb blue and red light and carotenoids absorb blue-green light (Figure 2), but green and yellow light are not effectively absorbed by photosynthetic pigments in plants; therefore, light of these colors is either reflected by leaves or passes through the leaves. This is why plants are green.
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