An illumination device for providing near isotropic illumination, and particularly an illumination system for detecting the defect in a transparent substrate and a detection system including the same are presented. An illumination system includes: an illumination system for detecting the defect in a transparent substrate, including light source receptacle in bar shape; first spot light sources, each emitting a respective first light, the respective first lights being substantially parallel to each other and the first spot light sources being arranged to a first line of spot light sources along the longitudinal direction of the receptacle; and second spot light sources, each emitting a respective second light, the respective second lights being substantially parallel to each other and the second spot light sources being arranged to a second line of spot light sources along the longitudinal direction of the receptacle.