This thesis was designed to evaluate the effects of environment conditions and planting densities on yield, morphology, heart formation, and nutritional content of romaine lettuce. Parameters considered were: planting density, day and night temperatures, and proportions of blue light within a mixed spectrum. Results showed a planting density of 30 plants per m² was optimal for the highest yield per area, while 10 plants per m² was optimal for the highest individual plant mass. A day/night temperature of 21/14°C resulted in the highest leaf curvature of heart forming leaves, and the most pronounced heart formation. Increasing proportions of blue light reduced plant fresh weight, height, and leaf area, while having no effect on the morphology of the inner heart. Twenty-two percent blue increased leaf sulfur concentration by 26 percent. This study has provided some of the key elements for romaine lettuce producers using a controlled environment.