Packaged LEDs and finished SSL products targeted at horticultural applications are finding an expanding market, reports MAURY WRIGHT, while scientists continue to try and match monochromatic spectrum to different plants and stages of growth.
Horticultural research has established that radiation at some relatively narrow spectral bands can optimize chlorophyll absorption in plants that in turn drives the photosynthesis process critical to plant growth. Both packaged LED manufacturers and makers of solid-state lighting (SSL) finished products are moving to capture a slice of what is a rapidly growing marketplace. Meanwhile, researchers continue to work to understand how other wavelengths might further boost productivity in greenhouses and indoor commercial plant farms.
The match between LED lighting and commercial growers of flowers and vegetables was a natural one. Whether in a greenhouse setting requiring supplemental light or an indoor setting relying completely on artificial light, electrical cost for the horticultural lighting has been among the major expenses for farmers. Energy-efficient SSL promised from the start to reduce the electricity bill.
|FIG. 1. Osram's new 730-nm LED can improve productivity for cultivators of peppers, tomatoes, and roses.|
But research into how specific spectral bands are primarily responsible for different stages of the horticultural growth cycle has made LEDs an even better fit for the application. A broad-spectrum source, such as a metal halide (MH) lamp, essentially wastes energy producing radiation in portions of the spectral band such as green, which has been shown thus far to have minimal to no benefit to plant growth. The monochromatic nature of LEDs, conversely, means that SSL manufacturers can deliver luminaires that solely produce the spectral energy that plants require, thereby adding to the energy efficiency.
Indeed, lighting-centric horticultural research is far from complete, but some principles are well established while researchers continue to discover relationships between specific spectral bands and vegetable or flower production. And LED manufacturers are reacting to the research. Osram Opto Semiconductors, for example, just announced what it calls a far-red LED centered at 730 nm to complement the hyper-red (660 nm) and deep-blue (450 nm) LEDs in the Oslon SSL family (Fig. 1).
Kim Peiler, LED applications manager for SSL at Osram, said the 450-nm and 660-nm bands have been well documented at this point as chlorophyll absorption peaks for all plants. New research, however, has demonstrated that the combination of 660- and 730-nm light can impact the phytochrome photoreceptor in plants. Peiler added that exciting the phytochrome pigment can make a plant flower faster.
Researchers are still studying how to apply the far-red light and at which points in the growth cycle. For example, Peiler said depriving a plant of the red light could simulate shade and result in a plant growing longer stems, useful for grafting. But at another phase in the growth cycle or in a different application, the red mix could quickly trigger flowering.
The mix of LED types in horticulture will continue to evolve. Osram also offers monochromatic orange, yellow, and green LEDs along with phosphor-converted white LEDs with which researchers are experimenting. Why a white LED, you ask? The blue pump in a white LED delivers the needed blue peak while white light is required for workers in a horticultural setting. So a mix of red and white LEDs could prove useful, providing the light needed by both plants and humans.
Horticultural lighting products
The market potential for horticultural SSL, meanwhile, is bringing new lighting manufacturers into the segment. For example, Hubbell Lighting just introduced the NutriLED horticultural lighting product family that utilizes 660-nm red LEDs and 460-nm blue LEDs (Fig. 2). Tom Veltri, Hubbell product manager for new product innovation, said the blue LEDs are key for the vegetative growth stage in a plant, while the red LEDs drive fruiting and flowering. Hubbell is using a two-to-one red-to-blue mix that Veltri said serves the broadest segment of the horticultural market.
We asked Veltri why Hubbell, a mainstream lighting manufacturer, made the decision to target the horticultural niche. Veltri said the market potential drove the decision. He noted that Hubbell research revealed a "number of growers with 1 to 2 million square feet of crops under roof."
The WinterGreen Research "LED Grow Light Market Shares, Strategies, and Forecast Worldwide" report, last released in April 2014, reported the 2013 market for LED grow lights at $395 million. But the report projects the market at $3.6 billion by 2020. Lux Research has said that in 2014 the market could be over $1 billion.
And there are reasons behind the market potential beyond the plant productivity and energy savings discussed earlier. Veltri mentioned the farm-to-table and organic food trends as a driver of indoor farming. He said, "Inside you can control the environment better for organics." And the farm-to-table premise essentially requires growers to operate near population bases. That means growing indoor crops in the winter in New England or the US Midwest, and in the summer in the US Southeast when outdoor temperatures may be too hot for many plants.
|FIG. 2. Hubbell launched the scalable NutriLED luminaires that can be cascaded in parallel configurations of linear fixtures.|
FIG. 3. The NutriLED luminaire includes an internal parabolic reflector that delivers a 60° beam pattern.
Veltri also discussed crop yield relative to minimizing the distance between the farm and consumers. He said yield loss happens during harvest, transport, and shelf life. Minimizing the transport time and distance cuts yield loss and extends shelf life.
Finally, indoor farms operate continuously and produce plants using a fraction of the acreage of traditional farms. With LED lighting, farms can layer plants such as lettuce or grow plants such as tomatoes 20-ft high. Such tomato crops might use interlining where LED strips are strung vertically to reach the vegetation along the length of the plant. The cool-running LEDs won't burn lettuce or tomato foliage even when placed within inches of the plant. Last year, for example, we covered a Japanese indoor lettuce farm using LED products from GE Lighting that produces 10,000 heads of lettuce per day.
Of course, horticulture does require some different luminaire design principles relative to general lighting. Hubbell designed the NutriLED horticultural lighting product to be scalable. The linear fixtures come in 2- and 4-ft versions and can be ganged together in a parallel fashion (Fig. 3) and linked end to end. Each fixture has an integral driver and Hubbell offers short power cords than can connect as many as 16 luminaires in a daisy-chain fashion to one AC power source.
Veltri also explained that Hubbell designed the optical system to deliver a linear 60° beam spread - much tighter than the lambertian pattern that is typical of high-power LEDs. The luminaire design includes a parabolic reflector within the extruded and anodized aluminum body and an acrylic lens on the face to protect the LEDs. Among other installation options, the design would enable fixtures placed between crop rows to both light the tops of plants and provide vertical illumination that reached the lower vegetation.
The 31W and 62W fixtures are designed to replace 400W and 600W HID lighting. The fixtures are designed for the relatively harsh environment inherent in horticulture with high humidity and temperature. The fixture is rated for 70,000 hours of life at 25°C ambient temperature, although it can be operated reliably at 50°C.
Greenhouse and specialty applications
Of course, the applications for LEDs in horticulture are not just indoors. Many greenhouses require supplemental lighting. Horticultural lighting manufacturer LumiGrow, for instance, recently published a case study in conjunction with Patterson Greenhouses in Broadway, NC. Patterson is using LumiGrow luminaires to extend the tomato growing season even in a relatively warmer part of the US.
|FIG. 4. Sprouts thrive under NutriLED lighting from Hubbell Lighting (top), while urban lettuce farms use LED fixtures developed by GE Japan Corp. to boost produce yield in a controlled environment (all other images).|
"If you average the amount of sunshine we receive each winter, it seems like we shouldn't require extra light," said owner Ryan Patterson. "If we have three cloudy days in a row, though, the plants don't get what they need so they don't grow as big or as fast. The tomatoes we have under the LumiGrow lights show more vigor than those that aren't."
Patterson has only installed artificial lighting in a third of his facility and has documented improved results under the LED horticultural lighting. He said during the earlier stage of plant growth, when thicker stalks are preferred, that the plants under the LEDs are 0.63 in. greater in diameter than the plants with no artificial lighting.
LED-based plant lighting is also scalable in terms of the size of the application. Consumers that are backyard gardeners can find LED-based grow lights just as can the largest commercial farmers. Sweden-based Heliospectra, for example, offers systems that also include water control for a broad set of customers. We recently wrote about a fine-dining restaurant in Sweden that is using such a system just to grow specialty herbs and produce.
Medicinal and legal marijuana
One other application segment lurks that could significantly expand the usage of LEDs in horticulture. The evolving acceptance of marijuana for medical or recreational purposes will lead to a significant uptick in legal indoor farms across the US and elsewhere. Arcview Market Research expects the legal marijuana market to more than quadruple by 2017 to $10.2 billion.
Illegal marijuana cultivators operating indoors have long favored LED lighting, although few people will speak on the record on the subject. Of course, low-power LED lights would save the cultivators on electrical costs. But LEDs also eliminate two ways that law enforcement can easily detect such operations. Law enforcement can work with power companies to detect urban and suburban locations including homes that are using excess energy. And HID lighting creates heat that can be detected by sophisticated thermal imaging instruments in helicopters, but LEDs run cool.
Heliospectra is one company embracing the application. The company recently said it had received an order for 1 million Swedish Krona ($119,300) from a customer in Seattle, WA. The same grower had previously ordered smaller amounts of LED horticultural lighting, and Heliospectra said it expects additional orders from the same customer and that it had sold smaller numbers of units to customers in Colorado and Washington where recreational marijuana is now legal.
The company said a typical marijuana crop can require a one- to three-month growing cycle depending on conditions. The aforementioned customer in Washington State was able to reduce the flowering cycle by one to two weeks, according to Heliospectra.
In reality, the potential for LED-lighting sales in horticulture is impossible to predict, especially with research uncovering new ways to use SSL to increase productivity. But just as the case with general LED lighting, growers have had some issues with LED technology. Hubbell's Veltri said, "Many growers have already had a bad experience with LEDs." Many early products did not meet specifications and came from small suppliers or overseas manufacturers that had little experience with complex SSL system design.
Still, the advantages of LEDs will lead most growers to adopt the technology at some point (Fig. 4). Osram's Peiler points out that applications such as close lighting of lettuce "are definitely only possible with LEDs." She added, "We definitely see more activity today."
The ongoing research is both a blessing and a curse. Academia may ultimately deliver different light recipes for every type of plant. About the LED choice and mix, Hubbell's Veltri said, "It all depends on the type of plant you are growing. They all use different portions of the spectrum." Apparently, the concepts of smart lighting and tunable spectrum may be just as important in horticulture as they are with humans.