This article details the design, construction, and operation of flexible system that modulates light exposure for the purpose of fabricating continuous and discrete gradient combinatorial libraries. Designed for versatility, the device combines "off the shelf" components, modular accessories, and flexible computer control, so that it can be used for a variety of combinatorial research applications. Salient aspects and capabilities of the instrument are illustrated through two practical examples. The first case demonstrates how user defined exposure functions can be used to create continuous surface energy gradient libraries with a linear profile. The second example illustrates the creation of continuous and discrete libraries for mapping exposure-property functions in a photocurable polymer system.