NOTE: End date changed to 08/31/2024 per D. Freeland/KSC. Original end date per NSSC information was 12/31/2023 (Ed., 10/5/23).

Two fully replicated, controlled-environment experiments were conducted using hydroponically grown red-leaf lettuce. The first evaluated temporal changes in light spectrum (quality), while the second assessed temporal changes in light intensity. Experiments were performed under both elevated CO₂ and ambient-Earth CO₂ conditions to reflect realistic spacecraft scenarios. Across both studies, the effects of temporal light adjustments were assessed in terms of plant growth, morphology, pigmentation (including nutritional value), and overall biomass accumulation.

Results indicated that temporal light adjustments can modulate plant development and resource use. Alternating light quality influenced leaf pigmentation and growth patterns depending on the timing and sequence of treatments. Temporal changes in light intensity allowed efficient photon delivery, supporting comparable plant growth to constant high light while reducing total energy input. Overall, dynamic lighting strategies demonstrated the potential to optimize lettuce production by balancing yield, quality, and energy efficiency, providing practical insights for space life support systems.

The project provided significant training and professional development. Undergraduate and graduate students gained hands-on experience in experimental design, hydroponic crop production, data collection, statistical analysis, and scientific communication. Two undergraduates conducted independent experiments, interpreted results, and presented findings at the 2025 American Society for Horticultural Science conference, earning awards in the Undergraduate Poster Competition. Other trainees contributed to technical support and experimental execution under the mentorship of the principal investigator, acquiring skills in controlled environment agriculture and research methodology.

Outreach and dissemination included professional conference presentations and local university events, highlighting the relevance of temporal lighting strategies for both space-based crop production and efficient indoor agriculture on Earth. Data generated have informed manuscripts currently under preparation or review.

Overall, the project successfully demonstrated that temporal modulation of light quality and intensity can enhance lettuce growth efficiency and nutritional potential. These strategies provide guidance for crop-specific lighting protocols in controlled environments, contributing to the advancement of space agriculture and efficient, high-quality indoor food production on Earth.

NOTE: End date changed to 08/31/2024 per D. Freeland/KSC. Original end date per NSSC information was 12/31/2023 (Ed., 10/5/23).

We conducted this experiment using four reach-in plant growth chambers with precise environmental control capabilities to maintain target levels. At the same light intensity (˜200 µmol·m-2·s-1), we tested four fixed light spectra (from seed to harvest) and four dynamic light-spectrum alternations, from combinations of blue, green, red, and/or far-red light. The dynamic light-spectrum alternations had light switching between the lag phase, the exponential growth phase, and the finish phase. We collected data on plant growth, morphology, coloration, and nutritional quality and analyzed data in statistical software, JMP Pro, using Tukey's honest significant difference test.

We found that low blue light in the lag and exponential growth phases, followed by short-term high blue light in the finish phase, improves lettuce nutritional quality without decreasing biomass as seen under long-term high blue light. Spectrum selection in the earlier phases should prioritize the photosynthetic photon efficacy of light-emitting diodes to maximize light use efficiency.

We are in the process of completing a second ground-based experiment, the objective of which is to characterize how alternating light quantity over time affects lettuce light use efficiency and final nutritional quality under elevated CO2 and moderate relative humidity. Several hardware-related issues from the plant growth chambers caused delays in completing the second experiment by now; however, they have been resolved through dedicated troubleshooting and testing. We plan to finish performing two replications of the second experiment by the end of 2024, and analyzing and visualizing all data by summer of 2025. A one-year no-cost extension is requested to ensure satisfactory completion of all aims in this project.