US Patent 10180529 Illumination device and light-guiding member

In one embodiment, an illumination device includes a light-guiding unit having a light output surface which outputs light and a back surface facing the light output surface, wherein the light-guiding unit has a curved surface in a region of the back surface farther than a first position on the back surface that is away by a first distance from an axis passing the light output surface and the back surface, and a rough surface in a region of the light output surface farther than a second position on the light output surface that is away by a second distance from the axis in a same direction as a direction from the axis toward the first position, and where an intersection of the axis and the back surface is an origin point, and a direction of the axis from the back surface to the light output surface is positive, a normal line of the curved surface intersects with the axis at the positive side of the axis, and an angle formed by a normal line vector at the second position in a direction toward the light output surface from the back surface of the light output surface and a vector in a direction from the curved surface to the second position is equal to or more than a critical angle.