Optimal and feedback control for light-based circadian entrainment

With the emergence of solid state lighting, light-based circadian rhythm control is becoming increasingly feasible. In this paper, we use a popular empirical model proposed by Richard Kronauer to study the entrainment with the light intensity as the control input. Given a reference circadian oscillation, we formulate the entrainment problem as a tracking problem: adjusting the light intensity to drive the circadian rhythm to the reference trajectory. We compare four cases: periodic light entrainment, active open loop optimal entrainment (using both the Kronauer model and a first-order approximation of only the phase response), active feedback entrainment, and subtractive feedback entrainment. Results from this study provide new insight and guideline to light intensity control for circadian rhythm regulation.