A projection system that can adjust color balance of incident light is provided. The projection system includes a light source, a spatial filter, an optical separator, a scrolling unit, a light valve, and a projecting lens unit. The spatial filter has a slit to adjust a divergent angle or etendue of light emitted from the light source. The optical separator separates light passing through the spatial filter according to color of incident light. The scrolling unit has one or more spiral lens discs, which are formed by spirally arranging cylindrical lens cells, rotate, and scroll color beams separated by the optical separator. The light valve processes light passing through the scrolling unit according to an image signal and forms an image. The projecting lens unit magnifies the image formed on the light valve and projects the magnified image onto a screen.