Patent ID: 7192174

Claim:
A light guiding panel which is made as a transparent substrate of a thin hexahedron shape and reflects source light that is incident through at least one side so that the light is emitted to a front surface of the substrate, wherein countless minute recesses are formed by a sandblasting method in random shapes on a flat bottom surface of the substrate so as to disperse the source light to be guided to the front surface of the substrate, where the sandblasting method is controlled to ensure that an injection amount of minute particles is constant with time through a process of forming the recesses so that the number of the minute particles impinging on a unit area of the bottom surface of the substrate in a unit time and the impact force on the bottom surface of the substrate by the minute particles gradually increase as a distance from the side, through which the source light is incident, increases, each of the recesses being too small to be seen with the naked eye and no visible light spot by each of the recesses appears on the front surface of the light guiding panel when the source light is incident through the side of the light guiding panel, and the countless minute recesses on the bottom surface of the substrate forming a gradation pattern such that the density of the minute recesses, the arithmetical average roughness Ra and the maximum height Ry of the bottom surface of the substrate, and the mean value of a contour size of the recesses gradual increase, as a distance from the side of the light guiding panel, through which the source light is incident, increases.