. ". 3B is a top plan view of the light controlling means segment of FIG. 3A dulyarranged in the spread illuminating apparatus of FIG. 1;FIG. 4A is a graph of a refractive index profile of the light controlling means segment of FIG. 3A, and FIGS. 4B to 4E are views of light tracks achieved by different refractive index distribution constants A.sup.1/2 set at the light controllingmeans segment;FIG. 5A" . . .