Energy-Efficient Supplemental LED Lighting Control for a Proof-of-Concept Greenhouse System

In this paper, a multiple-input multiple-output control system integrated with daylight harvesting is presented as a proof-of-concept system for energy-efficient greenhouse lighting. The control objective is to regulate the intensity of dimmable multispectrum light-emitting diode (LED) fixtures for achieving desired spectral irradiance levels and color ratios while utilizing the natural sunlight as much as possible. To ensure stability and improved dynamic performance, a Smith predictor is utilized to compensate for the delay introduced into the system by the communication hardware. A stability analysis of the closed-loop system is presented considering system delay and modeling uncertainties. The proposed control system was experimentally tested in a grow-tent environment consisting of dimmable halogen lights that emulate daylight variation, multispectrum dimmable LED fixtures, and low-cost light sensors. The results indicate that about 30% energy savings can be achieved by using the proposed automated lighting control system.