Red Light, Blue Light: Pros and Cons for Lettuce Production
April 17, 2025 At Cornell University, graduate students are studying the effects of far-red and blue lighting in indoor lettuce production. Neil Mattson, Ph.D., a CEA professor at Cornell, leads the lighting study. His primary goal is to increase energy efficiency and reduce energy costs in indoor farming by shortening the growth cycle of lettuce.
“We identified energy use within indoor farms as something we want to address,” he says. “LED lights are a lot more efficient than fluorescent and high-pressure sodium (HPS) lights. LED lighting brings us a lot of flexibility because we can adjust the light spectrum that we use and how much we get of each light color.”
Since about 14% of sunlight is far-red, Mattson explains, it’s essential for plant growth. However, he adds, most commercial growers today use white LED lights that are low in far-red light. As a result, their growing cycles are longer, usually taking between 45 to 50 days to produce a 5-ounce head of lettuce. In Dr. Mattson’s lab, where the lighting has been adjusted to have more far-red light, it takes only 35 days to produce the same sized head.
“Think about how many crop turns you have per year,” he says. “In 35 days, a grower could get through 10 turns in a year. Whereas in a 45- to 50-day cycle, it would only be about six or seven crop turns per year.”
But the lighting study did reveal some negative side effects. While far-red light produces larger heads of lettuce, they also appear less green and lose nutritional value. To counteract that, students have added blue light at the end of the crop cycle. “In our research, even just two days of high blue light at the end of the crop cycle was enough to give us some of those nutritional and color benefits,” Dr. Mattson says.
Based on what he’s seen in the study so far, Dr. Mattson encourages indoor growers to think about both the quantity and spectrum of light they’re giving their plants. “Consult experts to see if that light spectrum is matched for what your crop objectives are indoors,” he advises.
This article is a part of CEAg World’s Industry Report: Vertical Farming. Download the full report here: https://www.ceagworld.com/industry-reports/.