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The use of light-emitting diodes (LEDs) to support plant growth is a radical departure from use of gas-discharge lamps, which were developed in mid-19th and widely adopted by the industry during the 20th century. Initial investigation by the National Aeronautics and Space Administration (NASA) in the late 1980s on the use of LEDs to grow plant in space is resulting in an industry-wide transition from gas discharge to solid-state lighting systems. This global transformation is given urgency by national policies to reduce energy consumption and being facilitated by ready access to information on LEDs. The combination of research, government policy, and information technology has resulted in an exponential increase in research into the use and application of LED technology in horticulture. Commercial horticulture has identified the opportunities provided by LEDs to optimize light spectra to promote growth, regulate morphology, increase nutrient content, and reduce operating costs. LED-light technology is enabling the development of innovative lighting systems, and is being incorporated into large-scale plant factories for the production of edible, ornamental, and medicinal plants. An overview of prevalence of readily accessible information on LEDs and implications for future adoption in horticulture is discussed. LED technology is fundamentally altering the use and application of supplemental lighting for controlled environment agriculture. This paper provides a brief overview of the rapid development of LED lighting and some thoughts on the future application in horticulture. Carl Wilhelm Siemens tested electric carbon-arc lamps on plant growth in the mid-to-late 1880s and coined the term ‘‘electro horticulture’’ to define this application of electric lamps. He postulated that ‘‘the horticulturist will have the means of making himself practically independent of solar light for producing a high quality of fruit at all seasons of the year’’ (Siemens, 1881). Liberty Hyde Bailey, reporting experiments performed at Cornell University with electric carbon-arc lamps wrote ‘‘There is every reason, therefore, to suppose that the electric light can be profitably used in the growing of plants’’ and concludes with ‘‘On the whole, I am inclined towards Seimens view that there is a future for electro-horticulture’’ (Bailey, 1891). Both these predictions have been realized, with supplemental lighting being routinely used in commercial greenhouse production to promote growth and extend daylength. The advancements in horticulture lighting have closely followed refinements of this 19th century technology for modern residential and commercial lighting applications (Wheeler, 2008). NASA’s funding of research on use of LEDs as a light source for space-based plant growth systems in the late 1980s signaled the beginning of the transformation of horticultural lighting from high-intensity discharge lamps to LEDs (Barta et al., 1992; Wheeler, 2008). Scientists at the University of Wisconsin tested low-output red ( 660 nm) LEDs as lighting sources and demonstrated the feasibility of this fundamentally new approach to providing lighting for plants (Barta et al., 1990; Bula et al., 1991; Hoeghn and Luttges, 1990; Hoenecke et al., 1989). This led to the patenting of LED technology for plant growth in the United States (Ignatius et al., 1991) and LEDs were soon incorporated into instrumentation to study photobiology, photosynthesis, and plant physiology (Tennessen et al., 1994). NASA has continued to fund this research over the ensuing decades and the effects of LEDs on growth and productivity of a number of plant species has been reported (Goins et al., 1997; Kim et al., 2005; Massa et al., 2008; Mitchell, 2012; Morrow, 2008; Stutte et al., 2009). The technical advances in LED technology have increased output, electrical efficiency, and availability of wavelengths suitable for horticultural use (Stutte, 2009), enabling increases in research and commercial development, with several companies developing multiwavelength LED fixtures for the horticulture industry. The technical advancement in LED lighting is driven by consumer and regulatory demand to replace inefficient light sources in residential, commercial, and industrial applications (Morrow, 2008). Advancements have been so rapid and predictable that the Haitz model (Haitz and Tsao, 2011), which states that the amount of light generated per LED is increasing 20fold, and cost decreasing 10-fold, has been advanced to describe it. So how does this relate to horticultural research? First, there has been an explosion of research reports on application of LEDs in ornamental, vegetable, and nursery crops that has followed the increased output, decreased costs, and widespread availability of LEDlighting systems. Figure 1 illustrates the exponential increase in research for the 25-year period from 1990 to 2015. A general online search using criteria {‘‘Light emitting diodes’’ and ‘‘Horticulture’’} on a widely used digital search engine limited to academic sources (scholar.google.com, accessed 14 July 2014) returned 102 items (journals articles, patents, and journal citations) in the 5 years (1990–95) following the first reports of successful growth of plants under red LEDs. A decade later (2001–05), the same search criteria returned 1130 results, a 10-fold increase, and it’s on track to approach 10,000 articles, or over 2000/year, for the period from 2011 to 2015! The use of this search engine–based approach to assess research productivity is limited in that it may include duplication, is biased toward English language journals, and only searches articles indexed in Google Scholar (gudes.lib.umich.edu, accessed 12 Dec. 2014). While acknowledging the shortcomings of this approach with regards to providing a precise number of original research articles being published, Fig. 1 clearly illustrates that an exponential increase in information on LEDs to support horticulture is occurring. While to my knowledge, no systematic studies have been performed to assess the role of Internet in the adoption of LED technology by the industry, is clear that widespread access to the Internet, and effective tools to search and retrieve decentralized, remotely stored digital information (e.g., Mosaic, WebCrawler, Yahoo!, Google, and Bing) has been concurrent with the development of LED technology. These digital information tools provide commercial growers, along with the general public, easy access to cutting edge research that is unparalleled in history. Received for publication 1 Apr. 2015. Accepted for publication 3 June 2015. This paper was presented as part of the workshop ‘‘Advances in Commercial-ready LED Technologies for Horticulture’’ during the ASHS Annual conference, 28–31 July 2014, Orlando, FL. Author acknowledges the support of NASA’s Engineering Service Contract at the John F. Kennedy Space Center, Florida, and the Office of Research, Development and Enterprise, Limerick Institute of Technology, Moylish Park, Limerick, Ireland, of this work. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product and does not imply its approval to the exclusion of other products or vendors that also may be suitable. Corresponding author. E-mail: gary.w.stutte@ nasa.gov. HORTSCIENCE VOL. 50(9) SEPTEMBER 2015 1297 Widespread access to technical information, coupled with digital tools for distributing new or repackaged data via e-mail, user groups, video, and social media has arguably accelerated the pace of adoption of LED technology by horticulturists. The capacity for digital distribution of research results, and availability of the Internet to access this data, has resulted in the proliferation of research reports, field observations, and user experiences with LEDs being distributed to scientists, hobbyists, commercial growers, lighting manufacturers, and distributors. The amount of information available is staggering. A search (www.google. com, accessed 14 Dec. 2014) of ‘‘LED Lighting’’ resulting in an estimated 32,500,000 web pages! The following data provide a snapshot of this digital landscape, and are indicators of the power of digital media to disseminate information relevant to the commercial use of LEDs in horticulture. The proliferation of information on LEDlighting for commercial horticulture was illustrated by conducting a targeted Internet search of specific plant species. This was done by delimiting the search (www.google. com, accessed 14 July 2014) to ‘‘Light Emitting Diodes’’ and ‘‘{crop scientific name}’’ for five of species, Solanum lycopersicum L. (tomato), Lactuca sativa L. (lettuce), Petunia ·hybrida (Petunia), Triticum aestivum L. (wheat), and Cannabis sativa L. (marijuana) representing vegetable, ornamental, agronomic, and medicinal crops. This resulted in an estimated 124,000 web pages devoted to LEDs and tomato, 156,000 pages for lettuce, 180,000 for wheat, 690,000 pages for petunia, and in excess of 2 million for marijuana! The sheer volume of freely available information indicates that research on LEDs and plant growth, both professional and amateur, is being widely distributed and presumably informing decision makers on the selection and use of LEDs in horticultural production. This democratization of research and ease of access to information is exciting in that it provides the opportunity to accelerate the development and commercial adoption of LED lighting and to identify new and unique means of applying this technology. This explosion in information also presents a unique challenge to end users to accept the risk thatmisinformation is being perpetuated and acknowledge their responsibility to critically review information retrieved from online sources. It is not possible to establish exactly how much of the digital information is derived from, or distributed by, nontraditional research groups, but it is clear that a significant po

Commercial Transition to LEDs: A Pathway to High-value Products