What if indoor farmers could grow more lettuce without using more electricity? Researchers at Purdue University have found a promising answer hiding in a slice of the light spectrum most growers have largely ignored. Their study, published in the Journal of the American Society for Horticultural Science, shows that adding far-red radiation—the longest wavelengths humans can see, from 700 to 750 nanometers—to growing environments, combined with elevated carbon dioxide, dramatically boosts biomass in young leaf lettuce. The key is not blasting plants with more total light, but fine-tuning which colors that light contains. After 26 days of growth under controlled conditions, lettuce exposed to supplemental far-red accumulated substantially more biomass than plants grown without it. When far-red was paired with elevated CO2 at 800 micromoles per mole, the growth response was even stronger. The researchers used a total photon flux density of 400 micromoles per square meter per second—considered moderate for indoor farming—suggesting that growers can improve productivity not by cranking up energy input, but by managing the light spectrum itself. The mechanism is elegant: far-red wavelengths appear to stimulate leaf enlargement and improve canopy architecture, allowing plants to capture light more efficiently across their surface area. Elevated CO2 then amplifies photosynthesis, helping plants convert that captured light into more leaf material. At the young lettuce stage, these morphological changes did not negatively affect crop quality, making the approach especially relevant for baby-leaf and spring-mix production systems, where the target harvest is tender, fast-growing greens. The study was led by senior author Dr. Fatemeh Sheibani, a postdoctoral research associate at Purdue, whose work focuses on improving resource-utilization efficiency in vertical farming. It represents the second phase of a multi-year investigation into how environmental factors interact in controlled environments. The research is part of OptimIA, an initiative led by Michigan State University aimed at enhancing the productivity, profitability, and sustainability of indoor agriculture. As vertical farms and greenhouses expand to meet growing demand for locally grown produce, the findings offer a pathway to more energy-efficient crop production—one that relies on smarter environmental coordination rather than raw power. Cary Mitchell, professor emeritus of horticulture at Purdue who contributed to the work, has spent decades advancing controlled-environment agriculture technologies. His legacy and Sheibani's ongoing research suggest that the next leap in indoor farming productivity may come not from brighter lights, but from lights tuned to what plants actually need.