To provide an optical element that improves frontal brightness of a planar lighting device using planar lighting elements having isotropic light emitting characteristics.
A luminance improving film 5 is arranged on a glass substrate 10 of an organic electric field light emitting element 4 with the incident plane 6 closely stuck to the film 5. A plurality of projecting parts 7 is arranged on the opposite side of the incident plane 6 of the brightness improving film 5. A projecting part 7 is a circular truncated cone, and around one arbitrary projecting part 7, 6 pieces of the other projecting parts 7 are arranged so as to come into contact with the former one. The light made incident on the brightness improving film 5 almost vertically to the incident plane 6 is emitted from the top face 9 of the projecting part 7 almost without being refracted. On the other hand, the light made incident on the brightness improving film 5 tilted to the incident plane 6 is refracted so as to get closer to the normal line of the incident plane 6 on the ridge surface 12 of the projecting part 7 and emitted. Thus, the frontal brightness is improved.
ISOTANI BUNICHI
MITA YASUCHIKA
NIIDA HIDENORI
