FLAT LIGHT SOURCE DEVICE, LIQUID CRYSTAL DISPLAY DEVICE, AND LENS

摘要

Disclosed is a flat light source device comprising a light source unit further comprising a plurality of light emitting diodes and a lens that expands the light from the light emitting diodes. The light source unit lens further comprises an incident face, whereupon light from the light emitting diodes enters the lens, centering on an optical axis; and an exit face, wherefrom the light that enters the lens is expanded and exits the lens. The incident face further comprises a contiguous concave surface, and the exit face further comprises a contiguous convex surface. Additionally, with an angle ?i, which is formed by the optical axis and a line joining an arbitrary point upon the exit face of the lens and an origin point upon the optical axis corresponding to the location of the light emitting diodes, and a distance sagY, which is measured along the optical axis from the origin point upon the optical axis to the arbitrary point upon the exit face of the lens, when ?i is 0 degrees, sagY is designated sagY0, and sagY decreases from the maximum thereof at sagY0 as ?i increases. Excluding the vicinity of the optical axis, at ?min, which is when ?i, at the point where the curvature C of a very small region upon the exit face, on a cross-section that includes the optical axis, is at minimum, the exit face assumes a shape such that 10 degrees < ?min < 30 degrees.