Effects of light quality on growth and quality of lettuces in hydroponic

The effects of light quality on growth and quality of lettuce in hydroponic were studied. There were 3 treatments: white LED as control (CK), white-red LED (R: W=1:4) (T1), red-white LED (R:W=1:1) (T2) (red LED light 660 ± 20 nm). The PAR (Photosynthetically Active Radiation) was 150 μ mol.m
^-2
.s
^-1
, irradiation duration: 6:30-18:30. The lettuces were grown 35 days under different light treatment. The results showed that the growth and quality of lettuce were significantly affected by light quality treatment. The growth of shoot and root in hydroponic lettuce were enhanced by red light, and increased with the ratio of red light increased. The fresh weight of shoot increased by 34.6% and 52.7%, and that of root by 46.9% and 97.8% in T1 and T2 treatment respectively. And the dry weight of shoot increased by 40.3% and 66.7%, and that of root by 62.5% and 91.7% in T1 and T2 treatment respectively. The contents of soluble sugar and Vitamin C increased under red light, and increased with the ratio of red light increased. The soluble sugar concentrations in lettuce increased by 19.8% and 94.7%, and Vitamin C concentration by 76.7% and 97.4% in T1 and T2 treatment respectively. The nitrate concentrations decreased under red light, and decreased with the ratio of red light increased. The nitrate concentrations in lettuce decreased by 37.8% and 40.1% in T1 and T2 treatment respectively. Thus more red light is benefit for the growth and quality of lettuce in hydroponic.