an light device , includes a plurality of first light cells arranged axisymmetrically about an axis ; a plurality of second light cells arranged axisymmetrically around the axis ; and a controller coupled to a brightness adjust unit , and determines whether to activate the first light cells and second light cells according to a brightness adjust value of the brightness adjust unit , wherein the average distance between the first light cells and the axis is shorter than the average distance between the second light cells and the axis .