The sustainability of long-duration manned missions in space relies on plant-based Bioregenerative Life Support Systems (BLSSs). Providing optimal light conditions in closed environments is crucial for proper design and optimization of space-based plant growth chambers. Light-emitting diodes (LEDs) are a promising electric light source for BLSSs research due to their capability to control spectral output to meet specific crop requirements. In addition, controlling light quality permits direct stimulation of plant photoreceptors that can improve yield and nutritional attributes of food crops. The objective of this study was to quantify the effects of blue light on growth and morphology, physiology, and anatomical features of red lettuce (Lactuca sativa cv. 'Outredgeous') grown under different red-to-blue-light ratios. Five treatments were evaluated in this study: 100% red; 7% blue + 93% red; 26% blue + 74% red; 66% blue + 34% red; 100% blue. Treatment comparisons indicate that except for 100% blue, the increasing percentages of blue light resulted in decreased edible biomass production. In addition, stomata density decreased under monochromatic blue or red light, but no significant difference was found in stomatal limitation of photosynthesis.