Do you believe the Doctor who wrote the piece below where she mentions hot spots would mention them if they did not exist? If so why would a Doctor fib and claim hot spots exist when according to you they do not?
Bright Lights, Green Plants
by Dr. Lynette Morgan
Many growers choose to grow plants indoors using artificial lighting as the sole source of radiation for photosynthesis. Here's what you'll need to do it right
This is the third-part of a three-part article.
In the previous two articles in this series the basics of plant reactions to light, greenhouse lighting systems, effect of photoperiod and the economics of lighting were covered. This article delves more deeply into indoor lighting systems, both for commercial crops and smaller setups.
Indoor lighting for Hydroponic Systems
Often an inhospitable outdoor climate makes use of a greenhouse or outdoor system impractical or even impossible. A lack of natural light, very short day lengths, snow, ice, extremes of heat and/or cold can all make indoor cropping more economic in some areas then attempting to use a greenhouse structure. Other reasons for indoor gardening under lights may be practical- to grow some fresh, high-quality fruits and vegetables for the family in winter when outdoor space is not available or natural conditions limit growth so much that the whole project would be disheartening.
A flavorful winter grown tomato, fresh from the grow room, is an achievement many indoor gardeners strive for. Or, quite often, green-fingered enthusiasts just want a beautiful, relaxing indoor garden area in their home, office or work place that brightens up dull winter days or provides an oasis from everyday stress. In fact, indoor gardens with the correct type of artificial lighting can be used to treat folks with seasonal affective disorder (SAD) in winter. Some growers want an area where they can protect, grow and breed precious plants such as orchids or other exotics, without the uncertainties of climate, light and temperature that outdoor cropping can bring.
Indoor cropping can also be an economic option for some. A grow room garden is capable of producing fresh produce for sale such as cut flowers, herbs and salad greens, strawberries and other small plants are a good option in areas where fresh produce is expensive. Another important use of grow rooms, growth chambers or cabinets is in horticultural research. By being able to finely control all aspects of a plants environment, including dialing up what ever light levels are required, researchers can accurately measure and record plant responses. Crop research with artificially lit growth chambers that can be used to replicate any sort of climate on earth is widespread. Besides common hydroponic crops, plants as large as fruit trees, kiwifruit vines and even cereal crops undergo research in artificially lit growth chambers, allowing detailed experiments to be run year round.
The most attractive aspect of indoor cropping for hydroponic growers is the fact that even a very small area such as a workbench can become a fully operational garden producing a regular supply of fresh greens. Other household spaces such as a spare room or garage can be converted into a highly productive area that, with the use of artificial lighting, can produce an amazing amount of plant growth. On a larger scale, commercial producers have set up indoor systems in warehouses, converted refrigeration units or large cool stores and even grown crops inside caves, all making use of artificial lighting and hydroponic systems.
Perhaps one of the main reasons why indoor gardening has become so accessible to hydroponic gardeners has been the development and availability of highly efficient and effective horticultural lighting systems adapted to small spaces. Hydroponic retailers these days are experts in lighting systems for hydroponic gardens, and many offer detailed advice, calculations of lighting requirements and carry a huge range of equipment for the indoor grower. Since working through all aspects of creating the perfect indoor growing climate is a complex task, growers should take advantage of all the advice retailers have to offer in this area.
Designing Indoor Lighting Systems
Most grow rooms are created in a rather limited space, and many growers try to cram in far more plants than is practical to get the most from their lighting dollar. The first step with an indoor grow room lighting system is to plan what plants are to be produced, how large they will get at maturity, how much room will be required for other equipment such as fans, tanks and supplies. Remember to leave some space to be able to access all of the system. Then, armed with a floor plan, you can design the lighting system to make the most efficient use of the area.
The main point to consider is to plan the grow room lighting system so that the plants are still receiving sufficient light at maturity. In well-designed greenhouses, natural light comes into the crop from all sides, not just from above. The light is reflected up from the floor and pathways. Consequently, the entire crop canopy receives light, allowing large leaf areas to be actively photosynthesizing at once. In a grow room, lights are typically placed overhead, but for taller plants that are usually grown at a high density, some consideration of light penetration into the canopy is necessary, so consider installing light movers or side lighting. All light provided within the growing area also needs to be utilized and not wasted on unplanted areas, so reflectors and reflective surfaces become real energy savers.
Plants vary with regard to how much light they need to grow and develop optimally. Low light plants such as small seedlings may only need 10-15 watts per square foot. Many of the commonly grown hydroponic plants need approximately 20-25 watts per square foot, and some high light requiring plants need as much as 40 watts per square foot for optimum growth. The density of plants in the system and their eventual size also determines how many watts per square foot are ideal. Obviously, a single layer system of small, low-light plants such as lettuce needs much less light than a dense planting of indeterminate fruiting tomatoes that reach 6 feet at maturity.
Many indoor gardeners also consider the aesthetic lighting aspects of their indoor growing area to be just as important as plant growth, particularly where the area is used for offices or reception areas or for people's relaxation. Full-intensity HID lamps can be rather intense to the human eye without sunglasses; metal halides are easier on the eyes. Consequently, consideration of the lamp type, output, placement and direction is important.
Both metal halides and HPS lamps produce longwave radiation which results in a heat load that usually needs removal. Various methods of cooling can be used to remove this heat from an artificially lit growing area, and growers must take these into account when designing a lighting system. Water cooling is one method of heat removalÑwater-filled jackets have been designed which fit around lamps, removing much of the overheating problem. Ventilation and air movement becomes vital in some system to remove heat away from the plants while the lights are operating, and growers need to keep lamps at a safe distance above the plants to prevent leaf burnÑno closer than 1 meter for many bulb types.
Lighting for Indoor Grow Rooms
Lamps used most often in indoor gardens are fluorescents for seedlings and low-light plants, and the two main types of high-intensity discharge lamps: metal halide and high-pressure sodium.
Fluorescent LampsÑFull-spectrum and compact fluorescent lamps are best used for lower light requiring plants such as seedlings, herbs, houseplants such as African violets and small leafy vegetables or salad greens. Fluorescents are energy efficient and give off little heat, so they can be positioned close to the tops of the plants without causing any leaf burn. However, they have a lower output in general as compared to HID lamps and are best used for plants requiring 15-20 watts per
square foot of growing area.
Compact fluorescent bulbs come in 95-200 watts sizes, with a 200-watt fixture being suitable for a 2.5-by-2.5-foot growing area. For hydroponic growers who mainly use their grow room to raise early seedlings for outdoors or overwinter sensitive house plants, a small area lit with full-spectrum fluorescent tubes would be sufficient and a cost-effective option. These types of lamps are also suitable for a kitchen herb trough garden or additional window sill lighting. Many indoor gardeners also choose to have both a small area set aside with fluorescent lamps for germinating seedlings, rooting cuttings and growing small seedlings. They reserve HID lamps for over the main hydroponic system for larger, more mature plant growth.
High-Intensity Discharge LampsÑHID lamps consist of a sealed glass inner tube which contains a mixture of different gases. It's the blend of gases which determines the wavelength or color emitted by the bulb. There are two main types of HID lamps commonly used in indoor hydroponic gardensÑmetal halides and high-pressure sodium bulbs.
Metal halide bulbs produce much of their light output in the blue spectrum, which promotes vegetative growth and compact plants. Metal halides are often used where growers want the plants to look a natural, healthy color under a more white light that's easier on the human eye and for people to work around. Metal halides are a good choice for indoor salad crops, ornamental foliage gardens and displays in office and reception areas and where people might spend a lot of time. Newer types of metal halide bulbs include the daylight halides that allow plants to look as if they are bathed in natural light. These are popular for use in plant display areas where aesthetics are just as important as plant growth. Metal halide bulbs have a reasonably long life span, with an average of 10,000 hours usage. However, there is a gradual decline in light over time, and growers should monitor this with a reliable light meter to determine when bulbs needs replacing.
High-pressure sodium lamps produce more light in the orange/red wavelengths. This is why high-pressure sodium lamps are commonly chosen for greenhouse applications to supplement low levels of natural light, which contains sufficient amounts of the blue wavelengths, to give a good growth balance to the red wavelengths output of the sodium lamps.
HPS lamps are also more cost-efficient and have a longer life span, making them a more economic choice were natural light is available to provide the additional blue wavelengths. Indoors, where no artificial light is available to supplement in blue wavelengths, growers often use a mixture of lamp types for flowering plants or make use of conversion systems where the bulb can be switched as the plants reach flowering size, making use of the one bulb fixture.
Young, vegetative plants can be raised under only metal halide bulbs to promote vegetative growth. Boost photosynthesis with their higher spectra of photosynthetic photon flux in the 550-660 nm wavelengths. Growers then switch to HPS lamps as plants reach flowering maturity. However, this becomes complicated in systems where plants are at many different stages of maturity from young vegetative, through to flowering and fruiting, as many indoor gardeners prefer. For mixed-age systems, there are "hybrid" bulbs that can be used that provide the vegetative growth power of the metal halide with additional light in the red spectrum for flowering. For example, the Agrosun halide bulb puts out 38% more light in the red spectrum than regular metal halides, and the Son-Agro sodium bulb produces 30% more blue light than standard sodium bulbs.
Both metal halides and HPS lamps come in a range of wattage sizesÑ150-watt, 175-watt, 250-watt, 400-watt or 1000-watt. Systems usually consist of the lamp with attached reflector and ballast which is matched to the size of the lamp. The ballast may be either attached to the reflector, as in the case of the lower wattage bulbs. Or, in the case of the 400-watt and 1000-watt bulbs, remote ballasts are a separate metal box fixed to a wall.
The role of the ballast in a lighting system is to start and control the flow of electricity to the gas discharge light sources. It may also contain an igniter for HPS systems. Positioning and safe fixing of remote ballasts is another factor to take into account when designing a lighting system. The grower should ensure when purchasing individual lighting system components that the ballast wattage matches that of the bulb to be installed. Depending on the size and dimensions of the indoor growing area, better light distribution can sometimes be obtained from 2-3 evenly spaced, lower wattage bulbs than one larger wattage lamp, particularly where growers want to run both MH and HPS lamps at the same time for a more balanced wavelength distribution.
As a general rule, one metal halide bulb to 4-5 HPS bulbs will give enough light in the blue spectrum to even out the wavelength distribution. Light intensity from an overhead lamp is always most intense directly under the lamp and falls rapidly the further the distance the plant is from the bulb. Uneven lighting can lead to growth irregularities in mono cropping situations where only one plant type is being grown with taller, more advanced plants in the center directly under the lamp and lesser developed plants around the outer edges of the system where light levels are continually lower. In mixed cropping systems, growers can plan to have the highest light requiring plants closest to the lamp and lower light plants or shade plants on the outer edges of the growing area to give the best environment for both. Examples of plants which require high light levels are fruiting crops such as tomatoes, peppers, cucumbers, melons. Lower light requiring plants are those such as lettuce, many salad greens, some herbs, houseplants such as ferns and violets.
Light Movers
As a solution to the uneven light distribution pattern that indoor lamps can create, including patches of continual shade, over-intense radiation and hot spots, light movers have been developed for indoor gardening applications. Light movers have the advantage of not only spreading light but also dissipating more heat than a stationary lamp, meaning that lamps can be positioned slightly closer to the plants for higher intensity. Sources vary with regard to how much additional coverage a light mover system will allow compared to standard stationary lamps. Some say that as much as triple the area coverage is possible using a well designed lighting and mover system. Others state more conservative estimates. However, light movers can certainly allow a more even light distribution with only a small increase in energy consumption, giving uniform growth and reducing the risk of leaf burning and bleaching from stationary hot spots. There are many different designs of light movers. The main ones being based on either a straight track or light rail or circular designs. Some have a time delay incorporated in the design so the light may pause over certain areas, and many can carry more than one lamp at a time.
Reflectors
Choice of a reflector for an HID lamp may not seem that important so long as light is directed downwards onto the plants thus not wasting the 50% of light that's emitted upwards. However, the design, coating and placement of the reflector does influence the amount of light falling on the plants and its distribution significantly. George Van Patten found in a test of a number of reflectors, that "the best horizontal reflective hood yields as much as 40% more light than the worst vertical reflector" (Van Pattern, 199
. Consequently, growers should give some consideration to reflector design and its impact on light distribution. Many experts in the industry consider the double parabola reflector design, which consists of double arches, to be one of the most efficient reflectors for HID lighting. However, different reflectors have been designed for different bulb types, lamp placements and applications, and growers should seek advice on these when planning a lighting system.
Along with lamp reflectors designed to direct light downwards onto the plants, the surfaces of the indoor garden can also influence the direction, redirection, reflectance and absorbance of light. Any light that falls on a wall or floor or non-planted surface is essentially wasted, resulting in less energy efficiency in the growing area. Surfaces should be able to bounce light back onto the plants and preferably into the canopy where light from above may not penetrate.
At the same time, such surfaces should not create hot spots by intensifying light back into one area of the canopy where foliage burn could occur. Many indoor systems use white painted walls and floor coverings to create some degree of light reflectance. Other techniques include using a range of reflective films or foils such as Mylar which can be attached around the hydroponic system to reflect back as much light as possible. Growers can use a light meter to compare light levels inside systems before and after reflective materials are installed to determine just how much light "bounce back" they obtain.
Energy Efficient Lighting Systems
Raising energy costs are often a main concern for hydroponic growers wanting to set up an indoor garden, so obtaining the most energy efficient system possible is becoming increasingly important. Growers should take into account the cost of the lighting system, the cost of replacement bulbs, lifespan of bulbs before replacement as light output falls over time, cost of electricity to run the lamps and whether off-peak electricity rates can be used, and the energy efficiency of the type of lamp itself.
The cost of different lighting system packages and replacement bulbs can be easily determined and compared by shopping around the different hydroponic retailers and seeing what is available. Average lifespan of lamp bulbs or how often the manufacturer recommends they be run before replacement, is usually stated in product literature as cumulative hours, so a grower can estimate how often bulbs will need replacement based on the individual usage. As a general rule, HPS bulbs have almost twice the average life span as a metal halide bulb.
Energy efficiencyÑthe conversion of electricity into light outputÑis also different from MH and HPS lamps. This is typically measured as lumens per watt. Lumen is a unit of measurement of light output. Lamps are compared by the number of lumens per watt they produce as an indicator of efficiency. The more Lumens per watt the HID lamp produces, the greater the efficiency of the bulb.
HPS lamps typically produce up to 130-140 lumens per watt; MH up to 125 lumens per watt. Some hybrid bulbs can produce as much as 150-160 lumens per watt. Comparing that to a standard household incandescent bulb at 18 lumens per watt, the efficiency of HID lamps is far superior. Lumens per watt, however, does not give any indication of wavelength of light emitted by the lamp, so lamps of the same lumen output could, in theory, have very different effects on plant rate of growth and development. Thus, growers also need to take into account the different wavelengths or spectrum emitted when comparing lamps. Another, more accurate measure of lamp efficiency is PAR watts per square meter. PAR is short for photosynthetically active radiation. This gives an actual measure of plant-usable light output per watt.
How Much Will It Cost?
Running costs of a lighting system using HID lighting can be calculated relatively easily once the number of bulbs, their wattage and the price of local electricity is determined. The current cost of electricity per kilowatt/hour is given on electric bills. The process for working out the cost of running the lighting system is to multiply the bulbs wattage in kilowatts (kW) by the kWH rate from the local electricity supplier. For example, a 400-watt bulb is 0.4 kilowatt. Then multiply this answer by the number of hours per day the bulb is on and then by the number of days in the month to give the average monthly power cost of running the lighting system. If more than one bulb is in use in the indoor garden, then the running cost can be multiplied by the number of bulbs in use, or calculated for each individual bulb if different wattages are being used.
Some indoor growers are able to take advantage of off-peak electricity rates to significantly lower the running cost of their lighting system. Since plants growing only under artificial lighting don't need to stick to normal day/night periods, many chose to run the light period to take advantage of the cheaper electricity rates. Typically, cheaper, off-peak electricity rates are during the evening and night, so growers can save money by timing the lamps to give a maximum photoperiod at night.
Photoperiod in Grow Rooms
Having an indoor garden that is independent of and not reliant on natural lighting periods does have a major advantage when it comes to manipulation of photoperiod. Most plant species have an ideal photoperiod that yields maximum rates of growth and development. Increasing beyond this photoperiod usually gives no further increase in growth. Ideal photoperiod is species-dependent. Some plants need short day lengths to induce flowering while others need long day lengths. When the plants are mature enough to support flower development, growers can adjust the length of lighting per 24 hours. Some plants can grow happily under continual light; others may be damaged by this and many don't respond with increased growth once a maximum period of light per 24 hours has been reached.
Measurement of Indoor Lighting
Since the light output from HID bulbs tends to fall over time, light meters are essential tools for indoor gardeners, just as they are for growers using supplementary lighting in greenhouses. Light meters using various different units of measurement can be purchased from hydroponic lighting suppliers and at retail hydroponic shops. The best ones have an electronic readout and separate probe which can be used to obtain readings inside the canopy and in difficult to reach spots around the system.
Readings need to be taken in the same position each time to check the lamp's output as it ages. Light levels at the top of the canopy will be very different from those taken inside the canopy, and both should be checked from time to time. Growers with stationary lighting setups also should check for low light levels on the fringes. Low light levels there can limit plant production.
Future of Indoor Lighting
Development and research into more energy efficient lighting is continuing, and in the future we may be able to significantly increase the efficiency and output of lamps while further reducing the running costs. Two products under development are LED lamps, some of which are already on the market, and sulfur microwave lamps.
Research on using LEDs (light-emitting diode)Êlighting for hydroponic plant growth has been carried out by NASA in its space-farming systems for production of salad greens and other crops. LEDs are proving to be an efficient light source. Growers can custom-blend the red and blue light wavelengths for different plants and for different stages of maturity, thus little energy is wasted as light or heat. Also, LED systems also have much longer-lived bulbs. In theory this makes them cheaper to maintain than other types of lamps.
However, LEDs are more expensive than other lighting systems. Also, more research is neededÊinto the exact ratio of red to blue light for each crop and stage of development to maximize growth and energy efficiency.
NASA has also been trialling an even more efficient light sourceÑsulfur microwave lamps. These lamps are twice as efficient as other high-intensity sources and have been used to grow a range of hydroponic plants such as potatoes, sweet potatoes, lettuce, spinach, radishes, wheat, onion and others.ÊSince these lamps consist of a hollow quartz sphere with sulfur and argon gasses, there is no filament to burn out, and bulbs should last for many years.ÊHowever, the light put out by sulfur microwave lamps is so intense and bright that it is not really suited to small hydroponic systems and appears to have more potential in large greenhouse operations.
Dr. Lynette Morgan is a regular contributor to The Growing Edge. She holds a Ph.D. in Vegetable Production from Massey University, New Zealand.
For the complete version of this article, see The Growing Edge,
Volume 18, Number 3, January/February 2007, page 30.
http://www.growingedge.com/magazine/back_issues/view_article.php3?AID=180330
