Effect of Supplemental Light with Different Spectral LEDs on the Growth of Tomato Seedlings in North Greenhouse

The application of light emitting diodes (LEDs) for supplemental lighting is expected to increase quality of tomato seedlings in north greenhouse with less cost. Experiments were carried out to investigate the effect of supplemental lighting by LEDs with two different spectral qualities (blue, red and the combination of the two) on the growth of tomato seedlings. Plants were grown under different spectral light treatments for a month. The photosynthetic photon flux (PPF, 400-700 nm) at the top of plants was adjusted to 100 mu mol m(-2) s(-1). LEDs were used during the overnight period. The lighting was provided at a PPF level of 50 mu mol m(-2) s(-1). The air temperatures were kept between 18 and 26 degrees C. The relative humidity was maintained at 60% throughout the periods. The results showed that the growth of tomato seedlings was affected by the light quality of the overnight lighting. Particularly, Chlorophyll fluorescence parameters of tomato seedlings in solar greenhouse has change significantly, especially the value of fpsII parameter increased significantly under the combination of red and blue LEDs. It demonstrates that light energy conversion efficiency could be increased in this method.