A fluorescent substrate includes a base having a reflective surface and a flat bottom surface, and a fluorescent layer disposed on the reflective surface of the base such that the reflective surface of the base directs, outward from the wheel, fluorescence emitted from the fluorescent layer due to its excitation by exciting light. The reflective surface of the base has an array of minute reflective structures formed thereon so as to reflect, outward from the reflective surface, fluorescence emitted substantially parallel to the flat bottom surface of the base from the fluorescent layer.