Design and Simulation of a Circadian Lighting Control System Using Fuzzy Logic Controller for LED Lighting Technology

Abstract

This paper introduces a fuzzy logic-based circadian lighting control system using flexibility of Light-Emitting Diode (LED) lighting technology to synchronise artificial lighting with circadian (natural) lighting Correlated Colour Temperature (CCT) characteristics. Besides for vision acuity, the Non-Imaging Forming effects of lighting affect human circadian rhythms. Past works in spectrally tuning CCT or Spectral Power Distribution of lighting have used conventional Proportional-Integral-Derivative (PID) control system architecture, where the modelling process of system transfer functions was mathematically complex, especially for nonlinear systems. A methodology of regulating lighting CCT is employed in a 7×5 fuzzy logic rules matrix in a Fuzzy Logic Controller (FLC) system, to closely replicate natural lighting CCT characteristics for indoor lighting. A reference lookup table was devised to store desired CCT values arbitrarily with respect to time mark in a day, which acts as an outdoor circadian stimulus and guides the FLC. The FLC compensates for the lack of CCT in lighting space. Simulation results show acceptable CCT output values conforming to circadian lighting parameters at a time in a day compared to the lookup table targets. Deviation from blackbody curve was within ±0.003 using CCT Duv checking. The system did not produce an overshoot (0.0%) with a steady state (zero error) reached after the fourth iteration. Also, rise time was calculated to be 1 iteration. This approach could be further enhanced to cater for additional custom needs in many built environments. Future works may consider connecting more sensors to capture real-time outdoor CCT values for practical regulation.