For biomass production in a space-deployed Controlled Ecological Life-Support System (CELSS), efficient usage of limited resources such as light, CO2, growth area, and labor is more consequential than for biomass production on Earth. Light will be one of the most energy-consuming environmental factors to provide in CELSS. Therefore, development of an energy-efficient lighting-control strategy would make a great contribution to the sustainability of CELSS. Lettuce (Latuca sativa L.) was used as a model salad crop for the development of new control methods due to its rapid growth rate and high harvest index (≥80%). Lettuce seeds were sown and plants were cultured hydroponically in the Minitron II plant growth/canopy gas-exchange system. Canopy net photosynthetic rates (μmol CO2/m2 per s) were measured under a specific photosynthetic photon flux (PPF) and analyzed to decide the PPF of the next 1-h interval. Appropriate PPFs were provided on the initial day and during the first 1-h interval of each 20-h photoperiod. Plant-growth indices, crop yield rates (g/m2 per day), and power consumption rates were determined for different lighting strategies to identify the best compromise between energy cost and yield. Day/night temperature and CO2 concentration were maintained at 25/25C and 1100/400 μl·liter–1, respectively. This research is supported by NASA grant NAGW-2329.