Evaluating Light Sources for Hydroponic Production of Leafy Green Crops

As climates change and soil degrades across the globe, outdoor crop production in rich, fertile soil, -there- is a declining crop growing area, further compounded by a rapid increase of global population. This will necessitate an increase in food supply to meet this demand. The introduction of new technologies coupled with breakthroughs in science have allowed for mass crop production (not including roots or tubers) to shift indoors, abandoning soil and sunlight for water-based nutrient solutions and indoor lighting systems. What once was a methodical practice of forecasting and predictions has now become automation and precise calculations of nutrient concentration and light exposure. Hydroponic growing has many advantages over soil-based growing. This method allows growers more opportunities to control the environment, such as but not limited to, the duration and kinds of light used with crops. Photosynthetically active radiation (PAR) levels emitted by these lighting systems may greatly influence the crop’s success in the growing environment. Different lighting systems emit different amounts of PAR, which may result in significant growth differences in crops of the same species and cultivar and otherwise the same nutrients and other growing conditions. In this study, three growth cycle experiments were conducted over a 12 month period. All experiments were conducted indoors either in a greenhouse or growth room, using different cultivars of Romaine lettuce (Sunland and Chalupa, Monte Carlo, Dragoon) for each trial. As the crops grew, plant height measurements were taken as an indicator of crop growth under each lighting system. When the crop reached full maturity, all lettuce plants were harvested. Further measurements were taken postharvest, including shoot and root weight, number of marketable leaves produced by each plant, longest/median/shortest leaf length and width, and root length. Each growth cycle experiment was conducted over a 8-10 week period. PAR was measured for each lighting system using a 1 meter long integrating quantum photometer/radiometer. This research evaluates lighting system selection for optimum PAR levels to maximize crop yield and quality in indoor hydroponic crop production. It is hypothesized that the more PAR a light source emits, the taller plants it will produce, leading to higher crop yield.