Blue light requirements for crop plants used in bioregenerative life support systems

As part of NASA's Advanced Life Support Program, the Breadboard Project at Kennedy Space Center is investigating the feasibility of using crop plants in bioregenerative life support systems (BLSS) for long-duration space missions. Several types of electric lamps have been tested to provide radiant energy for plants in a BLSS. These lamps vary greatly in terms of spectral quality resulting in differences in growth and morphology of the plants tested. Broad spectrum or "white" light sources (e.g., metal halide and fluorescent lamps) provide an adequate spectrum for normal growth and morphology; however, they are not as electrically efficient as are low-pressure sodium (LPS) or high-pressure sodium (HPS) lamps. Although LPS and HPS, as well as the newly tested red light-emitting diodes (LEDs), have good photosynthetically active radiation (PAR) efficiencies, they are deficient in blue light. Results with several of the crops tested for BLSS (wheat, potato, soybean, lettuce, and radish) have shown a minimum amount of blue light (approximately 30 micromoles m-2 s-1) is necessary for normal growth and development. For example, the lack of sufficient blue light in these lamps has resulted in increased stem elongation and significant reductions in photosynthesis and yield. To avoid problems with blue-deficient lamps and maximize yield, sufficient intensity of HPS or blue light supplementation with red LEDs or LPS lamps is required to meet spectral requirements of crops for BLSS.