Greenhouses could be fertile ground for use of LEDs, and not just for the obvious reasons of low power consumption and little waste heat.
It turns out that different greenhouse plants can be ultra-sensitive to the wavelength of light they see. That sensitivity and the way a plant responds varies depending on the stage of the plant's growth. So research is now underway that aims to tailor LED output wavelengths to those that promote plant growth in ways that horticulturists desire.
In that vein, LEDs would be a step up from the incandescent bulbs that greenhouses sometimes use for illuminating growing plants. Incandescent light, for example, can make some kinds of plants have longer stems than what growers would like because they have a high far-red (FR) output. So a consortium was recently formed to research how LEDs and the various wavelengths they emit can augment plant growth. The consortium is especially looking at LEDs in greenhouse lighting. Institutions involved include the University of Arizona, Michigan State University, Purdue, Rutgers, and the Orbital Technology Corp. (Orbitec).
It turns out that scientists know a few things about different wavelengths of light can affect plant growth, but there is a lot more to learn. Researchers associated with the project recently described some of their work in a journal called Chronica Horticulturae. Among the areas they are examining for LEDs are lighting to induce early or out-of-season flowering and supplemental lighting to enhance photosynthesis for crop production, especially during light-limited periods of the year.
Interestingly, LED plant lighting is nothing new. LEDs were first used for sole-source plant lighting more than 20 years ago to grow lettuce. Seedlings grown only under red LEDs became elongated, but adding just a bit of blue fluorescent light solved the problem. Other species grown under LEDs include wheat, brassica (mustards), potatoes, and soybeans.
Among the factors consortium researchers are evaluating are the amount of red and FR light LEDs can give off and how these light wavelengths might be used to avoid stem elongation during the seedling stage and thus reduce time to flower (TTF) for some species. Researchers are also trying to induce flowering to get plants ready for predetermined market dates, using low-intensity (photoperiodic) lighting. Researchers think LEDs containing red and FR light will be as or more effective than conventional light sources at making plants with a photoperiodic flowering response flower.
Consortium researchers also have the idea of configuring vertical LED light towers so they straddle troughs within rows of high-wire tomato plants. They want to irradiate red and blue light in two directions within and along rows populated by tomato plants, rather than just beam light down from overhead. The thinking is that this will promote higher fruit yield by exposing more of the tomato plants to the right kind of light. In that regard, Orbitec fashioned light towers with LED panels that switch on or off incrementally with independent control of both red and blue LEDs.
The LED project website: http://leds.hrt.msu.edu/
The Chronica Horticulturae article is here: http://leds.hrt.msu.edu/assets/Uploads/LEDs-the-future-of-greenhouse-lighting.pdf
Orbitec LEDs: http://orbitec.com/store/led_lighting.html