Illumination system with plural light sources, and exposure apparatus having the same

摘要

Disclosed is an illumination system which includes a first optical system for combining plural light fluxes from plural light sources and for projecting the plural light fluxes to a surface to be illuminated, a second optical system for separating a portion of one of the combined plural light fluxes, and a first detecting system for detecting the light quantity of the portion separated by the second optical system.