LED greenhouse lighting is poised on the hockey stick of the adoption curve, saving electricity while potentially improving the world food supply.
The past year has seen production-scale deployment emerge out of years of trial grower installations, at users such as Rainbow Greenhouses in British Columbia, Clean Fresh Food in Wisconsin, Butter Valley Harvest in Pennsylvania, and many others.
The scale of modern greenhouse operations is visible in places such as Almeria, Spain, where greenhouses are actually changing the regional climate. In attempting to reproduce the energy flux of the sun over many acres, inefficient legacy lighting ends up drawing a staggering amount of electricity -- well into the megawatt range. There are growers that have to notify the local power company of their operating schedule. Lumigrow has a Canadian customer which operates its lights sixteen hours a day, seven months a year, and has a winter electricity bill that is ten times higher than it is in summer.
Growers also encounter local power caps. A commercial greenhouse complex in Indiana lost an entire summer’s worth of plants when its electricity was curtailed during a heat wave. To this should be added the approximately 1.3 quads (quadrillion BTUs) of energy spent hauling food, an amount nearly equal to the energy in the food itself. Roses and salad delicacies are hauled many thousands of miles to northern Europe, Canada, and Alaska, with the roses often transported by air.
LEDs have a unique efficacy advantage in horticulture. Plants appear green because they absorb red and blue, the bandgap energy of the two primary photosynthetic reactions. With LED lighting, the color of the light can be tuned to “horticultural red” (660 nanometers) -- deeper than the standard traffic light or brake light.
So why on earth has everyone been feeding plants orange high pressure sodium (HPS) light, the dominant horticultural lighting technology? The answer is that from a total output, lifespan and cost point of view, HPS used to be just the best of a bad lot.
Spherical emitters such as HPS lose up to 40 percent of their photons getting the light stream turned around in a downlight application. As with street lighting, LEDs have the advantage of being a natural downlight emitter.
PAR is for plants, lumens are for humans
An LED luminaire, for example, could put out red and blue photosynthetically available radiation (PAR) slightly greater than a standard 1,000-watt HPS luminaire, while consuming only 325 watts. The PAR unit of measurement is standard in horticultural lighting, since it is weighted for plant photosyntethic response. The lumen unit is useless in this context, as it is based solely on human visual response.
Obvious greenhouse lighting candidates are facilities located in cloudy northern areas with long winter nights. But any locale can employ year-round supplementation for especially light-hungry crops such as corn and tomato. There are a surprising number of tropical uses, including stretching the never-long tropical summer daylight, and the raising of crops that are intolerant of humid heat. All lettuce consumed in the tropics must either be grown in greenhouses or shipped in from a higher latitude.
LED horticultural lighting may yield one of the more financially viable greentech investment niches. Sector sales are growing rapidly, with market saturation still only in low-single-digit percents. While the total available market is respectable at $4.8 billion for North America, the far larger streetlight and residential lighting markets have distracted the attention of worldwide lighting majors and Asian exporters (with one or two significant exceptions).
Challenges include the technology's higher initial cost and the tendency of farmers to deliberate carefully before gambling an entire crop cycle on something new. Economics at present are channeling LED applications towards boutique areas such as flowers, seed stock growing, and salad herbs and delicacies. However, costs are falling. Payoff time is now often less than three years, and the latitude line for the viability of greenhouse lighting has dropped from Indiana southwards to Santa Barbara.
Beyond the energy savings, LED greenhouse lighting offers hope for continued technical progress in world food production. Observers such as Lester Brown and the Worldwatch Institute have noted that the years after the new millennium saw a reversal of some of the progress of the 1990s in eliminating world hunger. Drought in California is currently driving up food prices regionally; reportedly, the state government is considering diverting research funds to investigate greenhouse growing for saving water. The potential of LED lighting in the greenhouse is a bright spot for a hungry world.
Doug Widney is Manager of Engineering for LumiGrow, based in Novato, Calif. He has previously been a consultant in solar, batteries, and LEDs. LumiGrow, which recently achieved profitability, is funded by Clean Pacific Ventures. Reach him at firstname.lastname@example.org.