To provide an illumination system that reduces the power consumption of a luminaire by maintaining linear proportional relation between lightness of an illumination area and a mean pixel value of an image without reference to a range of lightness.

The illumination system comprises: an luminaire 1 which is installed on a ceiling surface and has its illumination area therebelow; a camera 2 which includes a part of the illumination area as its imaging area; and an illumination controller 3 which controls the luminaire 1 based upon the output of the camera 2. The illumination controller 3 comprises: a control portion 31 which controls the operation of the illumination controller 3; and an image processing portion 32 which sets effective pixels to be used to adjust a light control level according to respective pixel values of a picked-up image by the camera 2, and calculates a lightness index value based upon the mean pixel value of the effective pixels. Further, the illumination controller 3 includes a light control portion 33 which outputs a light control signal for adjusting the light control level of the luminaire 1 based upon the lightness index value that the pixel processing portion 32 calculates.