Physiological Responses of Baby Leaf Lettuce to Different Blue and Red Photon Flux Ratios Using LED As Sole-source Lighting

Light emitting diodes (LEDs) are increasingly used in ­­­controlled environment production as supplemental and sole-source lighting. As the effect of light on specialty crops is specific to each species, it is necessary to understand the impact of light on morphological and physiological traits of specific crops. Indoor-crop production via containerized growing (aka vertical farms) lacks standardized growing protocols including lighting requirements to optimize plant growth and morphology. The objective of this experiment is to evaluate different percentages of blue and red photon flux ratios under sole-source lighting using LED arrays in order to op­timize plant growth and reduce energy usage. Lettuce (Lactuca sativa) cv. Red Oakleaf was grown until the commercial harvest stage (average 70 g fresh mass) under 22° C average temperature, 30-50% relative humidity, ambient CO₂, 200 µmol·m^-2·s^-1 photon flux and 18 h photoperiod (daily light integral: 13 mol·m^-2·d^-1). Light treatments consisted of different percentages of blue (B) and red (R) photon flux ratios of 0B:100R, 10B:90R, 20B:80R, 50B:50R, 80B:20R and 100B:0R. Cool white florescence was used as the control treatment. Physiological plant responses such as fresh mass, dry mass, shoot and leaf length, leaf count, leaf area, anthocyanin concentration, chlorophyll concentration, visual quality, net photosynthetic rate, stomatal conductance, and nutrient content were collected and compared between the lighting treatments. The optimal light spectrum will be evaluated in terms of plant growth rate, plant morphology, and plant quality. In addition, the results will provide the estimated growing efficacy of each spectrum in terms of grams of produce per kWh of energy. Results will help determine which ratios of blue and red photon flux are most appropriate for commercial producers using LEDs in indoor growing systems.