The vegetable greenhouse industry in Quebec, Canada, was valued at approximately U.S. $50 million in 1999 with 12 ha dedicated to lettuce, representing ≈12% of the total greenhouse area that year (Carrier, 1999). Greenhouse production expanded greatly in the province in 1987 with the construction of 3.9 ha for tomato (Solanum lycopersicum), cucumber (Cucumis sativus) and pepper (Capsicum annuum) production under artificial lighting (Papadopoulos and Demers, 2000). The current situation for vegetable growers in Canada is challenging because of increased heating costs and costs of supplemental lighting required for year-round production.
The established practice for greenhouse growers interested in supplemental lighting technologies is to install HPS lamps and use them to extend the photoperiod of the crops to increase yields (McAvoy, 1984). However, this practice can be onerous for large installations, both in equipment and energy costs. Some other disadvantages of HPS lamps include heat generation and suboptimal spectrum for photosynthesis. LED lamps are a promising technology that has the potential to improve irradiance efficiency above HPS. Sustained developments in LED technology have brought their irradiance to a suitable level for being considered as a replacement to HPS lamps in hydroponics growth environments. LED lamps are anticipated to replace HPS lamps in most applications as a result of their reduced electricity consumption, improved quality of light, and the possibility for customization of the light spectrum for increased yields (Bourget, 2008; Morrow, 2008; Tennessen et al., 1994). Although equipment costs are still high, as is the case with most new technologies, growers across the world stand to substantially decrease their energy use, which directly translates into reduced costs for the greenhouse growers and reduced carbon emissions from the energy standpoint.
Earlier research reported that changes in irradiance wavelengths can result in changes in biomass production and morphology of plants because of changes in the ratio of the red/far-red spectrum (Brown et al., 1995; Heraut-Bron et al., 2001; Hoenecke et al., 1992; Taiz and Zeiger, 1998) and the effect of blue light (Hoenecke et al., 1992; Taiz and Zeiger, 1998). Moreover, changes in irradiance wavelengths can cause changes in the chlorophyll a/b ratio (Walters and Horton, 1995), chlorophyll biosynthesis and action spectrum (Anstis and Northcot, 1974; French, 1991; Koski et al., 1951; Ogawa et al., 1973; Virgin, 1993), β-carotene biosynthesis (Ogawa et al., 1973), and decreases in chlorophyll b under ultraviolet B light (Taiz and Zeiger, 1998).
Research has been performed to test the impact of light from LED lamps in several specific wavelengths, notably far-red, red, blue, and ultraviolet (Dougher and Bugbee, 2001; Okamoto et al., 1997; Yanagi et al., 1996). More recently, brighter diodes enabled their use as a potential replacement for traditional HPS systems in the 600- to 1000-W category of lamps (Steranka et al., 2002). Claims of 50% energy savings for similar biomass yields are now common in the marketplace (Craford, 2005). The aim of this study was to examine if LED lamps can produce similar biomass and phytochemical levels compared with HPS lamps at reduced energy cost for lettuce grown in a hydroponics setup.
Brown, C.S., Schuerger, A.C. & Sager, J.C. 1995 Growth and photomorphogenesis of pepper plants under red light-emitting diodes with supplemental blue or far-red lighting J. Amer. Soc. Hort. Sci. 120 808 813
Demmig-Adams, B. & Adams, W.W.I.I.I. 1992 Photoprotection and other responses of plants to high light stress Annu. Rev. Plant Physiol. Plant Mol. Biol. 43 599 626
Dougher, T.A.O. & Bugbee, B. 2001 Differences in the response of wheat, soybean and lettuce to reduced blue radiation Photochem. Photobiol. 73 199 207
French, C.S. 1991 Action spectra of photosystems I and II scaled by comparison of their sums with absorption spectra of photosynthetic plants Photosynthetica 25 67 74
Heraut-Bron, V., Robin, C., Varlet-Grancher, C. & Guckert, A. 2001 Phytochrome mediated effects on leaves of white clover: Consequences for light interception by the plant under competition for light Ann. Bot. (Lond.) 88 737 743
Hoenecke, M.E., Bula, R.J. & Tibbitts, T.W. 1992 Importance of ‘Blue’ photon levels for lettuce seedlings grown under red-light-emitting diodes HortScience 27 427 430
Johkan, M., Shoji, K., Goto, F., Hashida, S. & Yoshihara, T. 2010 Blue light-emitting diode light irradiation of seedlings improves seedling quality and growth after transplanting in red leaf lettuce HortScience 45 1809 1814
Kopsell, D.A., Barickman, T.C., Sams, C.E. & McElroy, J.S. 2007 Influence of nitrogen and sulfur on biomass and carotenoid and glucosinolate concentrations in watercress (Nasturtium officinale R. Br.) J. Agr. Food Chem. 55 10628 10634
Kopsell, D.A., Kopsell, D.E., Lefsrud, M.G., Curran-Celentano, J. & Dukach, L. 2004 Variation in lutein, B-carotene, and chlorophyll concentrations among Brassica oleracea cultigens and seasons HortScience 39 361 364
Koski, V.M., French, C.S. & Smith, J.H.C. 1951 The action spectrum for the transformation of protochlorophyll to chlorophyll a in normal and albino corn seedlings Arch. Biochem. Biophys. 31 1 17
Lefsrud, M.G., Kopsell, D.A. & Sams, C.E. 2008a Wavelengths from adjustable light-emitting diodes affect secondary metabolites in kale HortScience 43 2243 2244
Lefsrud, M.G., Kopsell, D.A., Wills, J. Jr., Sams, C. & Both, A.J. 2008b Dry matter content and stability of carotenoids in kale and spinach during drying HortScience 43 1731 1736
Ogawa, T., Inoue, Y., Kitajima, M. & Shibata, K. 1973 Action spectra for biosynthesis of chlorophylls a and b and β-carotene Photochem. Photobiol. 18 229 235
Okamoto, K., Yanagi, T. & Kondo, S. 1997 Growth and morphogenesis of lettuce seedlings raised under different combinations of red and blue light Acta Hort. 435 149 158
Papadopoulos, A.P. & Demers, D.A. 2000 The Canadian greenhouse vegetable industry with special emphasis on artificial lighting Acta Hort. 580 29 33
Shinohara, Y. & Suzuki, Y. 1981 Effects of light and nutritional conditions on the ascorbic acid content of lettuce J. Jpn. Soc. Hort. Sci. 239 246
Steranka, F.M., Bhat, J., Collins, D., Cook, L., Craford, M.G. & Fletcher, R. 2002 High power LEDs—Technology status and market applications Phys. Status Solidi 194 380 388
Stutte, G.W., Edney, S. & Skerritt, T. 2009 Photoregulation of bioprotectant content of red leaf lettuce with light-emitting diodes HortScience 44 79 82
Taiz, L. & Zeiger, E. 1998 Plant physiology. 2nd Ed. Sinauer Associates, Inc., Sunderland, MA
Tennessen, D.J., Singsaas, E.L. & Sharkey, T.D. 1994 Light-emitting diodes as a light source for photosynthesis research Photosynth. Res. 39 85 92
Virgin, H.I. 1993 Effectiveness of light of different wavelengths to induce chlorophyll biosynthesis in rapidly and slowly greening tissue Physiol. Plant. 89 761 766
Walters, R.G. & Horton, P. 1995 Acclimation of Arabidopsis thaliana to the light environment: Regulation of chloroplast composition Planta 197 475 481
Yanagi, T., Okamoto, K. & Takita, S. 1996 Effect of blue and red light intensity on photosynthetic rate of strawberry leaves Acta Hort. 440 371 376