The Search of an Optimized Supplemental Lighting Spectrum for Greenhouse Tomato Production

With ongoing, anticipated energy-efficiency improvements, as well as ever-improving light-distribution architectures, light-emitting diodes (LEDs) are a promising alternative to current supplemental lighting (SL) technologies for greenhouse crop production. Yet, significant opportunities remain to optimize spectral-quality effects on plant growth and development using LEDs to supplement sunlight in the greenhouse. The objective of this study was to compare different spectra of intracanopy (IC) SL using LEDs for high-wire greenhouse tomato (Solanum lycopersicum cv. Merlice) production in a mid-northern climate (lat. 40° N). Double-headed plants were grown in a glass-glazed greenhouse during a winter-to-summer production cycle in 2015. Five lighting treatments were evaluated in the study: natural solar light only (control); natural + SL from IC-LED towers using either 25% blue + 60% red + 15% far-red (25B-60R-15FR); 80% red + 20% far-red (80R-20FR); 10% blue + 90% red (10B-90R); or 30% blue + 70% red (30B-70R). An increasing solar daily light integral (DLI) occurred naturally for all treatments, and a constant DLI of 10.4 mol·m^‒2·d^‒1 (180 µmol·m^‒2·s^‒1 for 16 h d^–1) was provided to all plants grown with SL. Plant productivity, leaf gas-exchange responses, and stomatal density and index were measured for plants grown in each treatment. Preliminary results from this experiment will be presented.