Effect of the Intensity and Spectral Quality of LED Light on Growth and Quality of Spinach Indoors

In recent years, much effort has been devoted to understanding the response of plants to different light properties, largely due to advances in the light-emitting diode (LED) industry. This work studied the effect of different light intensities and qualities on yield or quality of indoor hydroponic spinach (Spinacia oleracea L.). Two trials were carried out at two different times. The intensity assay was carried out with the same type of light (AP673L, Valoya Ltd., Helsinki, Finland) at different luminous intensities (150, 290, and 430 mu mol m-2 s-1). In the second trial, four different luminance spectra (Valoya Ltd., Helsinki, Finland) were used (NS12, AP67, AP673L, G2). Then, the fresh and dry weight, nutritional status, and concentration of primary metabolites were determined. Both lights parameters induced changes in vegetative performance and other physiological traits, as well as their quality and nutritional composition (minerals, organic acids, sugars, and amino acids). The increase in light intensity increased Fv'/Fv', fresh weight, leaf area, chlorophyll fluorescence parameters, and potassium concentration. The light intensity effectively controlled nitrate accumulation in an inverse relationship. The effect of the light spectrum on spinach characteristics was not clearly observed when multivariate statistics were applied to the data. No linear relationship was found between the different R/B ratios. This is perhaps due to commercial lights having a complex combination of wavelengths, in addition to the main R/B proportion. Within the overall results, 6 R/B presented the best results for the indoor cultivation of spinach. More studies are needed, since breeding for controlled environments shifts the focus of the desired crop attributes towards rapid growth and harvest quality instead of stress adaptability.