Light emitting diode (LED) based systems are considered to be the future of lighting. We consider the problem of energy-efficient illumination control of such systems. Energy-efficient system design is based on two aspects: localized information of occupancy and optimization of dimming levels of the LEDs. Specifically, we are interested in minimizing the power consumption of an LED system, subject to providing uniform illumination at a pre-specified level around occupied zones, by determining the dimming levels of the LEDs. Localized occupancy information (i.e. occupied zones) is determined by an ultrasonic array sensor while providing a natural interface for illumination control. We present algorithms for localizing and tracking an occupant in an indoor environment. We show that the optimization problem for illumination can be solved by linear programming and use the simplex algorithm to determine the dimming levels. The efficacy of the system is evaluated with numerical simulations and experimental data.