Biofeedback Control for Optimizing Light Intensity on Plants Based on Canopy Level Chlorophyll Fluorescence Gain

Motivated by an increasing population and the desire to grow plants more efficiently, attention has turned to the use of Light Emitting Diodes (LEDs) to illuminate plants which are grown indoors. Indoor growing facilities enable closely controlled and mon- itored environmental conditions. More and more of these facilities exchange High Pressure Sodium (HPS) lamps for LED lighting since they provide more efficient lighting and the possibility to control light intensity and quality in order to illumi- nate plants with suitable light. However, most plants are grown under rather low, constant light regardless of the plants’ needs. Therefore, this work aims at develop- ing a procedure to use a response from the plants in a controller to provide optimal lighting for the plants. Optimal in this case means that the plants perform photo- synthesis at the highest light intensity which still allows maximum efficiency. To this end, plants are excited to give a fluorescence response of which the steady-state is studied. This signal is independent of the current incident light and used as control signal in a perturbation-based extremum seeking controller. The controller strives to locate and track the optimal light intensity which might be subject to changes in environmental conditions and plants’ health. By covering many important aspects of the proposed measurement procedure, this thesis provides the basis for further research in this matter.