This study was the second phase of a previously published study in which the interaction of these two important environmental inputs was investigated under a more limiting light level commonly used in commercial CEA. Under a light intensity of 200 mol m -2 s -1 , the CO 2 effect was more pronounced as a main effect. However, findings of the current study indicated that the effect of far-red is enhanced under a moderate total photon flux density of 400 mol m -2 s -1 . Biomass accumulation varied at different stages of development depending on the level of CO 2 at which lettuce was grown. While growers often focus on the amount of light delivered to crops, the study demonstrates that which wavelengths are included can be just as important as total light quantity.
Plants exposed to supplemental far-red radiation accumulated substantially more biomass than those grown without far-red. The growth response to far-red became even stronger when plants were also cultivated under elevated CO₂ concentrations. Together, the two factors promoted leaf expansion and foliar canopy development, allowing plants to capture light more effectively and convert it into plant material.
The research indicates that far-red wavelengths improve canopy architecture by stimulating leaf enlargement. Elevated CO₂ further increased photosynthetic efficiency, enabling plants to make better use of available light energy. Importantly, these benefits occurred without increasing total photon flux density, suggesting that growers can improve productivity through lighting-spectrum management rather than simply raising energy input.
Findings also suggest that far-red radiation influenced plant morphology in ways that did not negatively affect crop quality at the young lettuce stage, making the approach particularly relevant for baby-leaf and spring-mix production systems. Because lettuce is widely cultivated in vertical farms and greenhouses, the results provide actionable information for producers balancing energy costs with yield goals.
The study highlights the importance of integrated environmental control-coordinating lighting spectrum and CO₂ enrichment-to optimize plant growth. As controlled-environment agriculture expands, understanding how environmental factors interact will help producers refine production strategies and improve resource efficiency.
This research provides evidence that targeted spectral lighting combined with CO₂ management can increase yield potential in leafy greens production systems while maintaining moderate light levels, offering a pathway to more energy-efficient indoor crop production.
This study was part of a multi-institutional, multidisciplinary initiative called OptimIA (Optimizing Indoor Agriculture), led by Michigan State University and focused on enhancing the productivity, profitability, and sustainability of indoor crop production. Through this project and related research efforts, the Mitchell Lab at Purdue University has made significant contributions to improving resource- and energy-use efficiency in indoor farming. Optimization of environmental inputs investigated in this study represents a key strategy for increasing resource-use efficiency and, ultimately, advancing the productivity, profitability, and long-term sustainability of this rapidly expanding industry.
Cary Mitchell is Professor Emeritus of Horticulture and Landscape Architecture at Purdue University. His research contributions spanned controlled environment agriculture, plant growth regulation, and the development of advanced horticultural technologies.
Senior author, Dr. Fatemeh Sheibani is a Post-doctoral Research Associate at Purdue University. Dr. Sheibani’s main research topic is “enhancing resource-utilization efficiency of indoor farming”. With an emphasis on vertical farming, she has been focused on improving the energy-utilization efficiency of light-emitting diodes as the sole-source of lighting.
Additional contributors include Celina Gomez, associate professor of controlled environments at Purdue University, and Erik Runkle, professor of horticulture at Michigan State University, focusing on the environmental physiology of herbaceous specialty plants grown in controlled environments.
The full article can be found on the Journal of the American Society for Horticultural Science electronic journal website at: https://doi.org/10.21273/JASHS05550-25
Established in 1903, the American Society for Horticultural Science is recognized around the world as one of the most respected and influential professional societies for horticultural scientists. ASHS is committed to promoting and encouraging national and international interest in scientific research and education in all branches of horticulture.
Comprised of thousands of members worldwide, ASHS represents a broad cross-section of the horticultural community – scientists, educators, students, landscape and turf managers, government, extension agents and industry professionals. ASHS members focus on practices and problems in horticulture: breeding, propagation, production and management, harvesting, handling and storage, processing, marketing and use of horticultural plants and products. To learn more, visit ashs.org.
