Growing of leaf lettuce (Lactuca sativa L.) under high-pressure sodium lamps with supplemental blue, cyan and green LEDs

The aim of this study was to evaluate the effect of combination of light-emitting diodes (LEDs) and high-pressure sodium (HPS) lighting on the growth of lettuce variety ‘Multigreen 3’ in a greenhouse. Supplemental blue light had an impact on the efficiency of photosynthetic performance in lettuce; however, different blue light wavelengths had uneven effect. The 470 nm light also had a positive impact on chlorophyll a to b ratio and higher specific leaf area (SLA) value and resulted in increased plant mass per leaf area. The overall growth performance, higher contents of soluble saccharides and higher growth rates, represented by net assimilation rate (NAR) value were determined in lettuce, cultivated under blue 455 nm light. The 505 nm light, being intermediate between blue and green wavelengths, had a significant positive effect on the content of photosynthetic pigments, higher NAR value thus also might be beneficial for supplemental baby leaf lettuce illumination. Green 535 nm light stimulated accumulation of soluble saccharides in lettuce and had controversial effect on photosynthetic pigment contents and assimilative indices, thus the evidence for the effect was inconclusive.