Light emitting diodes (LEDs) are considered to become the dominant source of illumination in the future, offering long life times, energy efficiency and flexible tunability. The flexibility of adapting LED parameters offers multiple degrees of freedom in designing LED based lighting systems. In this paper, we consider energy-efficient illumination control design of LED based lighting systems in office spaces. Our goal is to determine the optimum dimming levels of the LED sources so as to minimize the power consumption while rendering (i) uniform illumination at a given illumination level in workspace regions that are occupied, and (ii) a minimum illumination level of lower value in unoccupied regions, while taking daylight distribution over the workspace plane into account. In order to determine occupant locations, we present an ultrasound array sensor solution with enhanced presence detection capability. We further propose a method to estimate and disaggregate illumination contributions of daylight and the different LED sources at the workspace plane. The performance of our proposed control solution is evaluated under different occupancy scenarios. (C) 2010 Elsevier B.V. All rights reserved.