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Lesson-2 PDF Print E-mail
Written by Administrator   
Friday, 07 October 2016 14:28



Lighting - Plant Grow Lights

Transpiration - Photosynthesis


Plants require a constant supply of energy to grow and this energy comes from light. In nature, plants receive light from the sun. In a classroom, you may need to add artificial light so your plants have an adequate amount of light to grow. There are various types of artificial lights that provide differing light spectrums. Before learning about these artificial lights, it is important to understand how plants use light in the growth process.

Transpiration and photosynthesis are the two major processes that are carried out by green plants that use energy from the sun. Both of these processes use large amounts of light energy but, only in photosynthesis is a significant amount of energy from light actually stored for future use. Light influences other processes such as flowering, seed germination, certain growth stages and pigment production but, in these cases, only very small amounts of energy from light are used.
During the transpiration process, plants draw in carbon dioxide from the air through their pores and water from their roots and give off oxygen and water vapor. Energy from the sun evaporates water from the plant cell walls. Although this results in a movement of water in the plant tissue (xylem), this energy is neither stored nor used to bring about vital reactions involved in the synthesis of foods, in assimilation, growth or reproduction.

In photosynthesis, which literally means "putting together (synthesis) by means of light (photo)", water is drawn up through the stem from the roots and into the leaf tissue where the chloroplasts, containing chlorophyll (a green pigment) can be found. There the water encounters carbon dioxide which entered the leaf from the air through minute breathing pores (stomata) located abundantly on the underside of the leaves. The stomata also permits the outflow of water vapor and oxygen. The light, carbon dioxide and water produce carbohydrates which are stored in the plant and later released as energy for other vital plant functions. Energy stored as chemical energy in foods (carbohydrates, fats, proteins) is continually released in living cells during the process of respiration. Basically, photosynthesis stores energy and respiration releases it, enabling cells to perform the work of living. By releasing energy, respiration provides the energy needed for all other plant functions. All animals ultimately depend on photosynthesis because it is the method by which all basic food is created.

Light Spectrums
White light, as it comes from the sun, is composed of waves of red light, through successively shorter waves to violet light. The band of colors that compose the visible spectrum of light (that which we can see) include, starting with the longest rays, red, orange, yellow, green, blue, indigo and violet. The visible spectrum represents only a part of the radiant energy that comes from the sun and only a part of the visible spectrum is effective in photosynthesis. Wavelengths exist that we our unable to perceive with our eyes. Beyond the red rays are still longer rays called infrared and beyond the violet rays are even shorter rays called the ultraviolet.

The fact that chlorophyll is green to the eye is evidence that some of the blue and red wavelengths of white light are absorbed, leaving proportionally more green to be transmitted, reflected and seen. Much of the red, blue, indigo and violet wavelengths are absorbed and used in photosynthesis while part of the red and most of the yellow, orange and green are barely used in photosynthesis.
Signs of Light Deficiencies in Plants:
- Plants will stretch and reach toward the light source
- Stem elongation
- Plant deformities
- No fruit set
Artificial Lighting: If your hydroponic garden is in direct sunlight, the plants should receive adequate amounts of light and absorb the spectrums they need.

In a greenhouse setting, supplemental light is sometimes used to extend the hours of light a plant receives during low light conditions (cloudy weather or short days), and to extend the growing season of a plant. If you are growing in an area with some, but limited sunlight, such as a windowsill, supplemental lighting will be needed. Any supplemental light is beneficial to increase plant growth and production. The higher the intensity and the broader the spectrum, the greater the benefit. You can grow in a completely enclosed space with no natural light if you provide all artificial light but there are several drawbacks including the cost of the lights and the energy to run them is high, there may be a compromise of the plants needs if the artificial lighting does not provide the complete light spectrum the plant needs and artificial lighting will not exactly duplicate the spectrum of light the sun provides.
There are four basic building blocks on which plant life is based: Light, Water , Nutrition, and Climate.
The most common factor that limits plant growth is the light source. Gardening outdoors, this obviously is not a problem; Mother Nature has seen to proper light balance and intensity for healthy plant growth. The responsibility for proper indoor lighting falls on the gardener. If your plants are not furnished enough light of the correct spectrum, they often will be mere shadows of what they could have been, if they grow at all. When you can't rely on Mother Nature to handle the lighting for you, the next best thing is a High-Intensity Discharge (HID) Metal Halide light system.

It is hard to compare HID lights with fluorescent tubes or incandescent light bulbs. Although they each create light from electricity, that's where the similarity ends. Fluorescent tubes emit a gentle, low temperature light in a very low wattage. Excellent for the first two weeks of most any plant's life, fluorescent lights simply do not provide the intensity of light required for most vegetables, flowers and ornamentals. Incandescent lights ('regular' light bulbs) are even worse for horticulture because they are very expensive to operate, put off as much heat as light, and do not offer the spectrums of light required for healthy plant growth. Even when incandescent light bulbs are altered with interior coatings to change their spectrum (like the "grow light" bulbs you see in the grocery store), they still do not come close to providing the kind of light a plant needs for robust, active growth. The only thing that will really grow and prosper under an incandescent grow bulb is your electric bill!

HID lighting systems represent the safest, most economical way of providing light for your plants. They are used all the time in parking lots, warehouses, baseball diamonds, football fields and other places where reliability and economy are a prime concern. Systems used for garden lighting are constructed differently, but the features of dependability and cheap operation remain the same. Two common types of HID lighting have been adapted for safe use in the garden and greenhouse, Metal Halide and High-Pressure Sodium.

Metal Halide light produces an intense light of a blue-white spectrum excellent for vegetative plant growth. Geraniums, marigolds, mums, zinnias, and violets all thrive under Metal Halide light, as do most vegetables. A plant grown under a halide light will often exhibit increased leaf growth, and strong stem and branch development. Roses grow hearty under metal halides, and seem to burst with buds before flowering time. A wonderful general purpose garden light, if your garden is to have only one light source, metal halide will be your best choice.

High-Pressure Sodium (HPS) light puts off an orange: shaded light which simulates the rich red hue of the autumn sun. Best as fruiting or flowering. lights, the HPS systems are often used In conjunction with metal halide for a complete balance of light spectrum in the garden. Flowers and vegetables finished off under HPS will show tighter, stouter blossoms with increased yields. HPS lights are commonly used in commercial greenhouses as starting lights and for supplemental light for off-season crops. Some types of plants respond particularly well to HPS lighting, such as the herbs dill and coriander.
Average Lumen Per Watt Output of Common Lamps
100 Watt Light Bulb 17.5 Lumens per watt
40 Watt Fluorescent Tube 22 lumens per watt
1000 Watt Metal Halide 125 lumens per watt
1000 Watt High Pressure Sodium 140 lumens per watt
Light Emitting Diodes: LED's can be very efficient with the lower end LED's being about twice as efficient as incandescent bulbs, and the higher end LED's have an efficiency just above the most efficient fluorescent lights. Recently specialized LED grow lights have come on the market with a balance of red/blue light for proper growth.
Besides being efficient LED have several benefits over other methods of lighting. LED's are very durable, they are solid state and are very hard to break by force. The lifetime of LED's is significantly longer. 35,000 to 50,000 hours of useable performance instead of 2000 for incandescent and 30,000 fluorescent.
Growlight LEDS may be costly initially, but have higher output and don't degrade when turned on.  

Go to: Lesson:3



Last Updated on Friday, 30 December 2016 13:50

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