Evaluation of lettuce growth using supplemental green light with red and blue light-emitting diodes in a controlled environment - A review of research at Kennedy Space Center

National Aeronautics and Space Administration's (NASA) Biological Sciences research group at Kennedy Space Center performed several experiments with lettuce, one of the Advanced Life Support candidate crops, to evaluate the effects of green light in a controlled environment. Lettuce showed similar growth and photosynthetic rates with the addition of 5% supplemental green light compared to the red and blue LEDs only grown plants. The addition of green light provided an aesthetic appeal of a green appearance. However, light sources with a higher fraction of green photons (> 50% of total PPF) resulted in the reduced plant growth. Among the levels of green photons tested, the addition of 24% green light (500-600) to red and blue LEDs enhanced plant growth. Spectral quality during growth affected the leaf photosynthetic rates (Pn) and the pattern of diurnal stomatal conductance (gs). The studies provided new information showing that leaf Pn and gs are responsive to spectral quality during growth and in the short-term, but are not directly coupled to dry mass accumulation.