An illumination system including light source elements including at least a first element for emitting a first color light and a second element for emitting a second color light whose color is different from the first color light. A screen receives the projecting light from the first and second color lights from the light source elements, and a plate is placed between the light source elements and the screen, thereby defining first and second areas, wherein the first and second areas have different properties of conducting light from each other. In this system, the first color light is projected through the plate on a first area of the screen and the second color light is projected through the plate on a second area of the screen. Then, the first and second areas overlap with each other.