An illumination system includes different color LEDs, a controller, and an input device. The controller controls intensities of the LEDs. The input device accepts an input corresponding to a total color of the LEDs. The input device includes a display, a pointer, and an output circuit. The display displays a chromaticity diagram. The pointer specifies a color point in the diagram. The output circuit detects the coordinates of the point and provides them to the controller. The controller includes a limiter, and a calculator. The limiter provides a limiter signal for limiting the maximum output the LED. The calculator calculates outputs of the LEDs based on the coordinates and the limiter signal so that the total color is adjusted to the point.