Dynamic lighting: intensity and spectral light modulation for improved plant growth outcomes within controlled environment agriculture

Abstract

The widespread adoption of Controlled Environment Agriculture (CEA), particularly vertical farming, remains economically constrained by the high energy costs associated with electric lighting systems. As modern light-emitting diode (LED) technologies approach their theoretical efficiency limits, further gains in energy performance must derive from innovations in the temporal and spectral delivery of light rather than from improvements in diode conversion efficiency. This dissertation addresses this challenge by developing and testing advanced strategies for precision lighting, specifically temporal and spectral modulation techniques aimed at improving plant productivity while reducing energy consumption. A custom, high-precision pulsed lighting system was designed and implemented to deliver photons at controlled intervals corresponding to plant photosynthetic and signaling kinetics. Commercial LED fixtures (RAYN Alina) were modified to allow external, independent modulation of each spectral channel. A dual-mode External Pulse Generator was developed, capable of operating in both microcontroller-based Pulse Width Modulation (PWM) mode and Field-Programmable Gate Array (FPGA) mode for arbitrary, high-speed light sequences with sub-microsecond precision. Plant electrophysiological responses were continuously monitored using the PhytlSigns biosensing platform, and growth was quantified via synchronized Raspberry Pi imaging units and a custom leaf area analysis pipeline. A central contribution of this research is the discovery of a previously unreported physiological regime in plant electrophysiology: sub-minute electrophysiological acclimation to fast light/dark cycles. This response, characterized by secondary electrical peaks during dark intervals, was observed across multiple species (Arabidopsis thaliana and dwarf sunflower) and found to depend on light frequency and intensity but not on certain spectral compositions. These dark-period signatures emerged consistently at slow pulsing frequencies (≤ 1/30 Hz), suggesting that very low-frequency light modulation (≤ 1 Hz) can induce stress-associated signaling rather than productive acclimation. Growth trials further explored the effects of high-frequency pulsed illumination (above the human flicker fusion threshold), including a complex color-sequenced regime inspired by U.S. Patent 20160014974A1 and a conventional PWM sequence (8.7 kHz). Across crops, both approaches yielded measurable, though moderately variable, growth enhancements. In tobacco seedlings, the color-sequenced regime at lower intensity (5.3 mol·m⁻²·day⁻¹) increased projected canopy area, while the PWM sequence produced consistent gains in biomass, chlorophyll content index (CCI), and canopy area across multiple trials. Electrophysiological measurements under the high-frequency sequence also suggested enhanced physiological stability in sweet corn compared to constant-light controls. Microgreen responses were species- and cultivar-specific: under the color-sequenced regime at lower intensity, amaranth ('Red Garnet') showed significant increases in leaf area and stem height, with modest, non-significant dry-weight gains, while basil exhibited shorter stems and arugula and radish displayed mixed effects. At higher intensity (9.5 mol·m⁻²·day⁻¹), 'Red Garnet' amaranth grown under pulsed light achieved a significant increase in dry weight (~11%) and a robust increase in stem height (~10%) without changes in leaf area, highlighting a reproducible morphological response to fast pulsing in this cultivar. Collectively, these findings demonstrate that the temporal dimension of light (its rhythm and structure) is as critical to plant performance as its intensity and spectrum. While slow pulsed lighting appears to induce stress-associated signaling, appropriately tuned fast pulsed lighting can sustain or improve growth efficiency at reduced photon flux densities. Future research should extend these experiments to physiologically optimal daily light integrals (DLI) to determine the scalability of dynamic lighting as a sustainable and biologically responsive strategy for next-generation CEA systems.