Effect of supplementary lighting of UV-B, UV-A, and blue light during the night on growth and coloring in red-leaf lettuce [Lactuca sativa]
2008
Ebisawa, M.(Central Research Inst. of Electric Power Industry, Abiko, Chiba (Japan)) | Shoji, K. | Kato, M. | Shimomura, K. | Goto, F. | Yoshihara, T.
In the case of hydroponics, the anthocyanin content of red-leaf lettuce decreases, and the poor coloring of a leaf occurs in many cases. We investigated the effect of irradiation for blue light, UV-A, and UV-B at night, in order to promote growth of hydroponic red-leaf lettuce and coloring. As a result, anthocyanin content increased using blue light or UV-B irradiation. Growth was promoted by blue light, but it was inhibited by UV-B irradiation. When simultaneous irradiation of blue light and UV-B was carried out at night, the anthocyanin content increased remarkably. Since it was necessary to reduce input energy as much as possible for utilization, light intensity, and a cultivation stage, which can promote both coloring and growth, were examined. Relevant optical irradiation conditions at night are described below. 1) Irradiate with blue light (9.4 W/square m) and UV-B (from 0.3 to 0.6 W/square m) simultaneously for 4 hours or more. 2) The most effective cultivation stage is one to two weeks before a harvest day. We showed that supplementary lighting was effective in the hydroponics of red-leaf lettuce.
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