Monday May 9, 2016
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.
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.