A great deal of current optical engineering development is centered on illumination applications. Designing optics to maximize photometric/radiometric output and uniformity are critical to low power consumption within portable or battery powered devices. Illumination optics can take the form of simple lenses, highly off-axis or aspheric elements, or even array-like structures. SPA is able to accurately model optical sources including LED's, lasers and arc-lamps, and their interaction with other types of optical components such as diffusers, reflectors and even mechanical structures. Some applications such as photolithography require extremely uniform illumination profiles to insure equivalent exposures over the entire field, so accurate modeling of these illumination systems is essential.