Assessment of Light Spectrum Effects on Lettuce Productivity under a Solar-integrated Hydroponic System

Abstract

The increasing demand for sustainable agricultural practices has suggested the need for innovative approaches like solar-powered hydroponic systems integrated with LED lighting. The objective of the study is to evaluate the effects of different red and blue LED light combinations on qualitative and quantitative parameters of lettuce and to assess the performance of solar-powered hydroponic systems in controlled environments. This study focuses on optimising lettuce cultivation at College of Agricultural Engineering and Technology, Godhra, Gujarat, India, by examining the impact of varying red and blue LED light spectra on growth and nutritional quality from August 2024 to February 2025. Four treatments were compared: T1 (50% Red - 50% Blue LED), T2 (25% Red - 75% Blue LED), T3 (75% Red - 25% Blue LED), and a control group grown under natural daylight with controlled monitoring of environmental and nutrient parameters. The concentration of phenolic compounds, important antioxidants in lettuce, was influenced by the light treatments. The T2 treatment (25% Red - 75% Blue LED) resulted in the highest average phenol content of 0.68%. The concentration of total soluble sugars, contributing to the sweetness of lettuce, varied among the treatments. The T3 treatment (75% Red - 25% Blue LED) exhibited the highest average total soluble sugar content at 5.5%. Ascorbic acid (Vitamin C) content, a crucial nutritional quality indicator, was significantly influenced by the LED treatments. The T2 treatment (25% Red - 75% Blue LED) resulted in the highest average ascorbic acid level at 15.4 mg/100g.  The percentage of protein in the harvested lettuce varied significantly across the treatments. The T1 treatment (50% Red - 50% Blue LED) resulted in the highest average protein content of 44.12%, significantly higher than both T2 and T3 (both at 42.28%) and the control group (40.44%). Chlorophyll content, a proxy for photosynthetic capacity, was highest in the T2 treatment (25% Red - 75% Blue LED) with an average of 2.1 mg/g fresh weight. Anthocyanin content, contributing to both the color and antioxidant properties of lettuce, was highest in the T2 treatment (25% Red - 75% Blue LED) with an average of 0.82%. Possible outcomes include optimized lighting configurations for maximizing lettuce yield and nutritional quality, with reduced energy consumption.  The findings could promote the widespread adoption of sustainable, energy-efficient hydroponic farming practices to address global food security challenges.