Effects of light intensity on the growth and leaf development of young tomato plants grown under a combination of red and blue light

We used red light-emitting diodes (LEDs, R) and blue light-emitting diodes (LEDs, B) to obtain the different light intensities of uniform spectra and investigated the effects of different light intensities on growth and leaf development of young tomato plants. The results showed that fresh weight, dry weight, stem diameter and health index were superior in plants grown under 300, 450 and 550 μmol m−2 s−1. The energy efficiency was highest under 300 μmol m−2 s−1. When photosynthetic photon flux density (PPFD) increased from 50 to 550 μmol m−2 s−1, a decrease in the specific leaf area (SLA) was observed. Under 300 and 450 μmol m−2 s−1, the thickness of leaves, palisade parenchyma and spongy parenchyma were the bigger, and the stomatal frequency and stomatal area per unit leaf area were also higher. The highest net photosynthesis rate (Pn) was observed under 300 μmol m−2 s−1. Our results implied that, compared to other light treatments, 300 μmol m−2 s−1 was more suitable for the culture of young tomato plants and there was no substantial gain from a PPFD above 300 μmol m−2 s−1.