Illumination and light sensing for daylight adaptation with an LED array: Proof-of-principle

Luminaires based on light emitting diode (LEDs) offer ease of control for light adaptation. In particular, adapting light output of the LED luminaires to daylight leads to energy-efficient lighting solutions. In a daylight-adaptive lighting system, the dimming levels are determined such that the artificial illuminance together with the daylight illuminance meets specified illuminance constraints. Closed-loop illumination control is traditionally used based on feedback obtained by measurements using light sensors, adding to cost and installation complexity. In this paper, we present a solution wherein the LED luminaire is used as a light source as well as a light sensor. We propose a protocol wherein the LEDs are driven in forward-bias by a pulse width modulation signal, thus emitting light, and in reverse-bias over a duration where they sense light. Under the proposed solution, the sensed illuminance is solely the daylight contribution. This enables use of simple open-loop illumination control schemes for daylight adaptation. We demonstrate the proof-of-principle with an LED array prototype.