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Radish (Raphanus sativus L.), green onion (Allium fistulosum L.), and lettuce (Lactuca sativa L.) are among several “salad” crop species suggested for use on the International Space Station (ISS) as a supplement to the crew’s diet. Among the more important factors affecting the crop yields will be the light intensity or photosynthetic photon flux (PPF) used to grow the plants. Radish (cv. Cherry Bomb), green onion (cv. Kinka), and lettuce (cv. Flandria) plants were grown for 35 days in growth chambers at 8.6, 17.2, and 26 mol m−2 d−1 (150, 300, or 450 μmol m−2 s−1 PPF, respectively) with a 16 hr photoperiod and cool-white fluorescent lamps and either 400 or 1200 μmol mol−1 CO2. Final (35-day) edible yields were taken for the treatments under ambient or supplemented CO2. Results showed a response of growth to incident PPF that indicated a strong influence of lighting on yields.