Since their development in the mid-1960's, the luminous efficiency and range of available output wavelengths of light-emitting diodes (LEDs) have increased to such a degree that an enormous number of new applications for LED sources are now being pursued. For these applications, it is critically important to design the illumination optics to achieve high flux-transfer efficiency. In this paper we describe a nonimaging projection lens design to efficiently collect and transfer flux from a Hewlett-Packard LED source to a rectangular target at a distance from the Led and tilted with respect to the lens' symmetry axis. The source was experimentally characterized using a technique that captures its full four-dimensional luminance distribution. The lens was then designed by implementing a constrained global optimization procedure over a parametrization search space with variables that determine the positional and aspheric geometrical properties of the lens. The optimization was performed subject to constraints arising from packaging and fabrication considerations. The resulting lens employs a combination of refraction and total-internal reflection (TIR) mechanisms to achieve a total flux-transfer efficiency of 40%.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.