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LED plant lighting applications

Life science applications, high power LED has brought revolutionary advantages, such as in the field of horticulture, LED obvious advantages, performance in energy efficiency, low / no maintenance, spectral control and beam control. However, plants need to get different things from light, while some metric, such as efficacy (lumen / w / w) or CRI, may or may not provide the desired results for plants and flowers. In addition, plants and humans are different, they have circadian circulation, and the differences between the plants.
 
However, in the greenhouse, especially in urban or vertical farms, growers are rapidly turning to the use of solid state lighting, horticultural practitioners are also studying the needs of plants, hoping to open a different "light recipe" to get the most Good plant growth and yield.
 
1 Solid state lighting in the role of gardening
 
The use of LEDs in fruit and vegetable agriculture is mainly to extend the growing season, especially in the cold regions of the summer. In the past, artificial lighting for plant growth was mainly high pressure sodium (HPS). However, one of the obvious advantages of LED-based solid-state lighting is that lighting does not generate heat, and growers can use interactive lighting, that is, place light in the middle or side of the plant, illuminate the lower part of the plant vertically or horizontally The
 
However, the greatest impact of the LED is the growth of green leafy vegetables and herbs, because these can only grow to measure the height in inches, and can grow on the shelf, each shelf has a dedicated set of LED lamps near the plant. This layered shelf is very common in so-called cities or vertical farms, occupying only relatively small growth spaces in buildings near the population center, while the best lighting and technology, including hydroponics, To achieve a shorter growth cycle.
 
 
 
Figure 1 Chicago's Green Sense Farms in its vertical farm
Planting micro-vegetables, lettuce, beets and so on
 
2 City Farm
 
In fact, LED lighting may have the greatest impact on the horticulture of urban farms. Growers grow in large quantities of vertical farms in the city, which means that transportation costs will be reduced and consumers will be able to eat on the day of harvesting in some cases, and the shelf life of the products will be longer. Agricultural carbon emissions will be greatly reduced as transport is shortened and no mechanical equipment is needed for traditional farming.
 
LED gardening on the benefits of consumers is more and more. Consumers can get more fresh products, so the taste is more sweet. In addition, urban farms are generally free of pesticides, and production may not even need to be washed because they are usually grown in a clean medium in a water culture rather than in dirt. Later, the method of planting tends to be water-saving, especially in arid areas or areas where groundwater and / or soils are contaminated.
 
3 gardening lighting challenges
 
Of course, there are challenges in any emerging technology, LED-based gardening lighting is also a challenge. At present, the experience of solid-state lighting technology is still very shallow, and even engaged in years of gardening scientists are still studying the plant's "light formula", the current "new recipe" in some of the impracticable.
 
Rami Vardi, general manager of Canoga Park Lighting Manufacturing, said that Asian lighting manufacturers are positioning the market is usually affordable but low-end products, many low-end products on the market lack of certification, such as UL grade, and LM-79 lamp report And the LM-80 LED report. Vardi said that many growers had early attempts to deploy LED lighting, but because of poor lamp performance, feel very frustrated, so high pressure sodium lamp is still the industry's gold standard.
 
Of course, there are many high-quality lighting products on the market, including Philips, OSRAM and Hubble lighting. OSRAM and Philips spent years studying horticultural studies with university and specialized research organization teams.
 
However, gardening and floral growers still need better measurement standards related to the application. For example, the American Society of Agricultural and Biological Engineers (ASABE) Commission on Agricultural Lighting will begin to develop standardized metrics in 2015. This work is taking into account the metrics associated with the PAR (Photosynthetic Active Radiation) spectrum. The PAR range is usually defined as a spectral band of 400-700 nm, where the photon actively drives photosynthesis. Common measures associated with PAR include photosynthetic photon flux (PPF) and photosynthetic photon flux density (PPFD).
 
4 "recipe" and metric
 
The "recipe" and the metric are intertwined because the grower needs to measure the standard so that it can recognize whether the fixture provides the intensity and spectral power distribution (SPD), which includes the "recipe".
 
Early studies focused on the absorption of chlorophyll in the spectral power relationship, since chlorophyll is the key to the photosynthesis process. Laboratory studies have shown that the energy peaks in the blue and red spectra match the absorption peaks while the green energy shows no effect on absorption. The early results of the study resulted in excess pink or purple light on the market.
 
However, the current idea is focused on lighting that can provide peak energy in the blue and red spectra, but at the same time can emit a wide range of lighting like sunlight. "The industry seems to be moving toward white light," said Paul Scheidt, head of product development at Cree LED.
 
5 white is very important
 
Neil Yorio, vice president of biology innovation and optimization systems (BIOS), commented that "using only red and blue LEDs is out of date, and when you see the spectrum of products, it is based on older science that is often misunderstood" "The reason why people choose blue and red is that these wavelength peaks are consistent with the absorption curves of chlorophyll a and b separated in the test tube, and today we know that the light of all wavelengths in the PAR range is useful for driving photosynthesis. Doubt, the spectrum is important, but it is related to the shape and shape of the plant.
 
Yorio's view is that studies show that we can change the spectrum to influence plant height and flowering results. Some growers constantly adjust light intensity and SPD, because plants do have something similar to circadian rhythms, and most plants have unique rhythms and "recipe" requirements.
 
Spectrum King's Vardi says the main red and blue combinations may be relatively good for leafy vegetables such as lettuce. But he also said that for flowering plants, including tomatoes, its strength is stronger than the specific spectrum. Vardi said 90% of the energy in the high pressure sodium lamp is in the yellow area, and lumens (lux) and lux (lx) in the flowering plant gardening fixtures may be more accurate than the PAR-centered indicators.
 
Spectrum King uses 90% phosphor in its lamps to convert white LEDs, and the rest is red or far red. Vardi says the blue LED-based blue lighting provides all the blue energy needed for the best production.
 
 
 
Figure 2 The traditional form of high pressure sodium lamp
 
6 "recipe" and influence
 
In addition to the basic production conditions of green leafy vegetables, white light is important. Many people interviewed said that if there is no light of some of the green band, lettuce may be immature and does not look green. On the other hand, sometimes growers can control the spectrum to produce new colors. For example, Gus van der Feltz, director of global agriculture at Philips Lighting, said that growers may wish to grow red with lettuce and the blue energy peak in white LEDs is a favorable factor.
 
Obviously, there is no consensus on the "light recipe", researchers and growers are also constantly strive to promote scientific development. Colangelo said: "We are constantly studying the light recipe for each breed." Philips van der Feltz said that each plant's formula is always different, but added: "You can adjust the growth process." In the plant's growth stage , Changing the light may cause significant differences in the same plant. "We changed the light every hour," said Matt Vail, co-founder and chief operating officer of Local Roots.
 
 
 
Figure 3 Local Roots container farm, which is equipped with LED lighting system
 
"Light recipe" the development process is very difficult. Philips' van der Feltz said the company's research team had studied various strawberries in nearly a year and used different red, magenta, blue and white blends. But after a long effort, the team finally found a "formula", in the better taste and juiciness reached a 20% gap.
 
7 What do growers want?
 
With the commercial LED lighting gardening equipment gradually mature, manufacturers for the needs of growers will be more clear. Green Sense's Robert Colangelo thinks there are 4 points. First of all, Colangelo wants high quality products to maximize energy efficiency. Second, he wants a lighting product that can use different combinations of light for each breed. Colangelo says Green Sense has found that changing the lighting dynamically during the plant growth cycle does not benefit, but requires a different "recipe" for each species. Third, the lamp is easy to install. Fourth, Colangelo argues that economic affordability and financing are important because he says the lights are the most expensive elements of vertical farms.
 
Not all business growers can find what they need from commercial LED lighting manufacturers. For example, Local Roots designs and starts manufacturing custom rectangular LED fixtures. The company is equipped with a used transport container that can accommodate a complete farm with a capacity equivalent to 5 acres of traditional farms. Local Roots uses DC to power its lamps, relying on a single AC circuit. Vail said that the design mixes monochrome and white LEDs, and custom control systems can achieve 0-100% control of each LED's strength.
 
Of course, many urban farmers have stressed that the gardening problem requires a system-level approach beyond lighting. These large urban farms usually achieve complete environmental control by computer temperature and humidity measurement, and control hydroponic feed and lighting.
 
Moreover, these businesses have developed new areas. For example, Green Sense uses a unique growth medium made from coconut shells. A New York area farm called AeroFarms (Figure 4) produces a custom substrate or growth medium made from recycled water bottles. And, AeroFarms uses the so-called jet mist system, the company says the water used is 40% less water than the hydroponic system.
 
 
 
Figure 4 AeroFarms farm in New York area
 
 
 
Figure 5 Philips Lighting GreenPower LED production module
 
The company said the module includes red, far red, blue and white LEDs that dynamically provide the plant with the primary color needed for the plant
 
 
 
Figure 6 Innovatus Farm in Fuji, Japan
12,000 lettuce can be produced per day
 
 
 
Figure 7
 
▲ A French tomato farm uses Philips lamps between rows of plants to provide the desired spectral energy to the lower leaves of each plant
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