Light-emitting diodes in horticulture

Light-emitting diodes (LEDs) have great potential to revolutionize lighting technology for the commercial horticulture industry. Unique LED properties of selectable, narrow-spectrum emissions, long life spans, cool photon-emitting surfaces, and rapidly improving energy use efficiency encourage novel lighting architectures and applications with promising profitability potential. In greenhouses, such unique properties can be leveraged for precise control of flowering and product quality for the floriculture industry, for energy-efficient propagation of ornamental and vegetable transplants, and for supplemental lighting of highwire greenhouse vegetable crops for all-year production. In a sole-source lighting mode, LEDs can also be used for transplant production, as well as for production of rapid-turning vegetable and small fruit crops. Evidence is accumulating that nutritional and health attributes of horticultural products may be enhanced by specific wavelength combinations of narrow-spectrum light from LEDs. During periods of seasonally limited solar light, LEDs have potential to enhance daily light integral in greenhouses by providing supplemental photosynthetic radiation, particularly of red and blue light. The cool photon-emitting surfaces of LEDs permit their novel placement relative to crop foliar canopies, including closecanopy overhead lighting as well as within-canopy lighting, which greatly reduces electrical energy requirements while maintaining adequate incident photon fluxes. Because of the small size of individual LEDs and narrow beam angles from LED arrays, light distribution can be highly targeted and waste of light from LEDs minimized compared with other light sources traditionally used for horticulture. Prescriptions of spectral blends (e.g., red:far-red and red:blue ratios) can be developed for LEDs to accomplish specific photomorphogenic goals for seedling development, flowering, and possibly yield and produce quality. LED light quality may also be useful to control pest insects and to avoid physiological disorders otherwise caused by low-intensity or narrow-spectrum lighting. Complex factors such as rapidly improving LED luminous efficacy, favorable mass-manufacturing costs, local costs of electrical energy, and capital investment will interact to determine for which applications and when LEDs become the dominant lighting technology in horticulture.