Kuraray Co., Ltd.

Kozo Yasuda

Toshiyuki Yoshikawa

Osamu Shinji

Toshitaka Kunisawa

A lightguide which guides light from at least one side end plane and includes a plurality of approximately trapezoidal protrusions whose apex edge in the cross section perpendicular to the axis of a linear light source has a partially straight section. The approximately trapezoidal protrusions are arranged on the rear surface of the lightguide, opposing a light emitting surface. The approximately trapezoidal protrusions are arranged in a pattern of specks, solid lines, or broken lines. The pattern has a low area density in a region neighboring the at least one side end plane and at a high area density in a region removed from the at least one side end plane such that the luminance distribution of the light emitted from the light emitting surface is approximately uniform. Preferably, the approximately trapezoidal protrusions have, in the same cross section, two rounded corners, and the roughness of the surface that includes the apex edge of the protrusions, the roughness of the rear surface excluding the protrusions, is less than 0.2 &mgr;m, the ratio of the height H to the width W of the approximately trapezoidal protrusions in the same cross-section be 0.1&lE;H/W&lE;0.6, and the width W is 20 &mgr;m&lE;W&lE;200 &mgr;m.

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Ibaraki, Japan

Kozo Yasuda