Biosensor, based on canopy-level chlorophyll fluorescence, for improving lamp light use efficiency in controlled environment agriculture

Paper in proceeding, 2025

While all environmental factors that drive crop growth are being controlled and monitored in high-tech greenhouses, there are no sensors commonly used that can directly monitor plant performance and well-being. Chlorophyll fluorescence is an interesting signal to monitor in that regard as it is closely linked to photosynthesis. It is also well studied in plant science. However, most conventional approaches of measuring chlorophyll fluorescence are based on high-intensity flashes of light, and therefore difficult to apply in a production environment. In this study, we tested a novel canopy-level fluorescence sensor for the application of monitoring light use efficiency threshold (LUEt) for improving lamp light use efficiency. A greenhouse trial on lettuce, with and without drought treatment, was conducted, followed by a similar trial in an indoor production environment. The results indicate fluctuations in LUEt, or more specifically, the LUEt-proxy fluorescence-based measure, throughout different times of day and growth cycles. LUEt typically exhibits elevated levels during the day and diminished levels in the evening. LUEt is higher in the middle of the growth cycle than in the beginning or end. Furthermore, LUEt drops upon drought stress, seemingly before visual symptoms appears. As a final touch, a LUEt control algorithm, tracking and adjusting to LUEt light level, was implemented and tested. It showed potential and revealed challenges. The study concludes that monitoring LUEt via chlorophyll fluorescence yield measurements can be used as a tool to optimize lamp use, screening strategy and to detect stress, also in a production environment.