ABSTRACT
In practice artificial light sources being widely used in horticultural crop growth are high-pressure sodium lamp, metal halide lamp, fluorescent lamp, incandescent lamp and so on (Bugbee, B., 1994; Horaguchi, K. and Morita, M , 1987), but they provide inappropriate light spectrum and cannot promote crop photosynthesis comprehensively. Moreover, the disadvantages of these light sources are low luminous efficiency, electricity-consuming, short life span, large size and not easily controlled. With the remarkable progress of material science, semiconductor technology and manufacturing, as a new type of light source light-emitting diode (LED) can be available with high power and provide reasonable spectrum and enough light intensity (Masamoto, T. et al. 1995,1996). Therefore, it can be used to supply light for horticultural crop (Okamoto, K., et all995. Yanagi, T., et all996, 1997). In recent years light-emitting diode and laser diode (LD) have been developed, but the latter is much more expensive and can not produce comprehensive spectra for green plants. LED can provide large fluxes of red photons and so could be used to make lightweight, efficient lighting systems for photosynthetic research. (Tennessen, D.J., Singsaas, E.L. and Sharkey, T.D., 1994). An illumination facility for greenhouse plant cultivation was designed with the dominating 640 nm photosynthetically active component delivered by AlGalnP LEDs and supplementary components from AlGaN and AlGaAs LEDs. Photosynthesis intensity, photosynthetic productivity and growth morphology as well as chlorophyll and phytohormone concentrations were investigated in radish and lettuce grown in phytotron chambers under the LED-based illuminators and under high-pressure sodium (HPS) lamps with an equivalent photon flux density (Tamulaitis, G., et al., 2004,2005). Using red LEDs alone and powered with AC is feasible for the commercial production of Zantedeschia plantlets in vitro. A flexible light source, entitled LEDSet, was developed suitable for the research on photobiological responses of plantlets in vitro and for the young plant production (Jao, et al. 2003.2005). Different peak wavelength LEDs which are respectively at 400nm, 450nm, 655nm were chosen to compose a lamp to provide light for plants.General energy ratio of the three types of LEDs is 22:46:33, which could promote plant photosynthesis. (Feng Chunyuan, Feng Hongnian and Jin Shangzhong, 2005). For the practice, an American company LICOR has successfully developed LED pack for the photosynthesis measuring system, which can be controlled within 2000 umol/ m2.s and meet with the requirement of photosynthesis experiment. For further study on the supplemental light effects of LEDs on horticultural crop, appropriate quantitative proportion of red and blue LEDs is most important. Meanwhile, to provide even light intensity distribution, spatial deployment of red and blue LEDs need to be studied. A new type of LED artificial light source device is developed for seedling and cultivation, which could reduce the use-cost and improve economic benefit. This paper mainly deals with the light-supplementing effects on horticultural crop with the LED artificial light source.
