Minimum Light Requirements for Indoor Gardening of Lettuce

Abstract

Indoor food‐gardening is an important trend in horticulture. However, most research‐based light recommendations are oriented towards commercial production, with recommended daily light integrals (DLI) significantly higher than those found inside a home environment. The objective was to evaluate growth (fresh and dry mass), accumulation of key phytochemical constituents (leaf photosynthetic pigment and nitrate content), and aesthetic quality (elongation and pigmentation) of red‐leaf lettuce (Lactuca sativa) grown from transplant to a harvest stage in an indoor environment using different (i) light sources (light‐emitting diode [LED] vs. fluorescent lamps), and (ii) light quantities (from 1.6 to 9.7 mol m−2 d−1). In the first experiment, four broadband white light sources were compared in a growth chamber using 5.2 mol∙m−2∙d−1: (i) ‘neutral‐white’ 4000‐K LED lamps, (ii) ‘day‐white’ 5000‐K LED lamps, (iii) ‘neutral‐white’ 4100‐K fluorescent lamps, or (iv) ‘daylight’ 6500‐K fluorescent lamps. Lettuce grown under LED lamps produced more shoot fresh and dry mass than those grown under fluorescent lamps. However, all light sources resulted in comparable growth and quality attributes. In two separate experiments, plants were grown under one of four DLI. As DLI increased, plants had more growth, higher aesthetic quality (more compact leaves and higher pigment content), and superior nutritional quality (increased leaf concentrations of anthocyanin and carotenoid, and reduced nitrate). Based on these results, a minimum DLI of 6.5 to 9.7 mol m−2 d−1 is recommended when designing indoor gardening systems for red‐leaf lettuce plants.