by DRAKE STALIONS
LIGHT-EMITTING diodes (LEDs) have long been recognized for their distinct benefits over traditional lighting technologies. Benefits such as long life, energy efficiency and flexibility in design and application have led designers to choose LEDs for a myriad of lighting applications.
The evolution of LED technology over the past decade has been remarkable, with the LED and the solid-state lighting (SSL) market growing significantly over the past several years. However, when compared to the rest of the lighting industry, the introduction of LEDs into horticultural applications is much more recent and has only materialized over the last one to two years.
The introduction of LEDs into the horticultural market is largely due to significant advancements in LED technology that allow for the manufacturing of high-power packages in specific wavelengths. Greenhouse operators and other commercial growers can benefit greatly from the energy savings and improved efficiency that LED lighting can deliver.
For plants to grow well in a greenhouse environment they need the correct temperature and the right light to allow for the optimal absorption of chlorophyll, the primary pigment responsible for photosynthesis and plant growth. In recent years, academic studies have proven that plants are more sensitive to particular wavelengths of light and demonstrate increased chlorophyll absorption and photosynthesis when exposed to red (~640 to 660 nanometers) and blue (~450 nanometer) light. These studies have shown that the light absorption spectral peaks for chlorophyll fall within the ranges of 400 to 500nm and 600 to 700nm, as demonstrated in Figure 1.
Light Emitting Diodes vs. High-Pressure Sodium
High-pressure sodium (HPS) lamps are the most commonly used light source for supplemental lighting in greenhouses. Comparing the spectrum of HPS lamps with the chlorophyll absorption peaks shows that most of the light output from HPS lamps falls outside the peak absorption ranges of the chlorophyll. Also, a typical 2-acre greenhouse using HPS lamps will consume about 10,000 mega watt hours of electricity per year. Research has found that only 7 percent of light created by HPS lamps is absorbed by plants, and much of the energy created with these lamps is wasted due to inefficiencies.
By converting from HPS to LED lighting, energy savings can be achieved. In addition to the energy savings, using LEDs with specific spectra designed to match the peak absorption wavelengths of chlorophyll can ensure that the light output is much more effective in stimulating photosynthesis and plant growth. By utilizing state-of-the-art, energy-efficient LED technology, there is a significant opportunity to stimulate plant growth through the use of targeted wavelengths, while drastically reducing energy consumption.
Improvements In LED Technology
LED manufacturers have recognized the huge potential benefits for LED lighting in horticulture. Thanks to advancements in the technology, it is now possible to deliver high lumen output within a very compact package, which is ideal for clustering many LEDs into one small luminaire.
By designing luminaires to utilize a combination of LEDs at the two wavelengths closest to the peaks of the chlorophyll absorption spectra (455nm and 660nm), it is possible to achieve greenhouse lighting that realizes an increase in healthy plant growth and a simultaneous decrease in energy consumption.
A recent pilot project to test the replacement of conventional greenhouse light sources with special wavelength LEDs has yielded a 40 percent reduction in energy consumption and a 20 percent reduction in chemical fertilizers used for healthy plant growth. Further advancements in LED diode technology are also having a positive impact, and LEDs are expected to achieve 45 percent efficiency for 455nm and 660nm wavelengths by the end of 2011
Implementation Of LED Lighting
Greenhouses and growers in the horticulture industry are starting to employ LED lighting using several different methods. LEDs can be used to conserve energy in traditional ceiling lighting, as well as multilayer cultivation (modular vertical layers) and inter-lighting (between or among plants). Multilayer and inter-lighting can be particularly advantageous in stimulating plant growth and reducing energy consumption as the light can be more closely directed at the plants, with less light and energy lost to the surrounding environment.
Many traditional lighting technologies cannot be used for these methods of lighting as they emit too much heat, which can be damaging to the plants. It is estimated that the LED horticulture lighting market will reach roughly $20 million by 2013 for LED components alone, mostly in multilayer cultivation and inter-lighting applications.
Other Positive Impact & Future Possibilities
Recent studies have also shown that certain wavelengths and color temperatures of light can increase the amount, weight or biomass of fruit and vegetable production in certain plants. By using more predefined light, the joules spent per kilogram of produce is reduced. With the right combination of light, it is possible to increase plants’ yield by more than 20 percent, while also improving produce quality and lengthening the production season.
Other wavelengths also contribute to increased photosynthesis rates and plant growth, and research is being conducted to investigate the positive effects of additional saturated wavelengths of light, including infrared (IR), to stimulate plant growth at various stages of the growing process. By further advancing LED technology and our understanding of how particular wavelengths influence plant processes and growth, it may be possible to revolutionize the horticulture industry.
About the author: Drake Stalions is marketing and business development manager of solid state lighting, OSRAM Opto Semiconductors.