To optimize a combination of a luminaire with a polarizing plate in consideration of refractive indexes of three axes or crest-directional, array-directional and thickness-directional axes of a prism to improve front brightness and light extraction efficiency.
In the luminaire or a liquid crystal display device, a prism sheet 11 with a plurality of prisms 11P having first-directional crests Pr continuously arrayed in a second-direction orthogonal to the first direction on one surface is disposed between the polarizing plate 6 and a light source. Assuming that the crest-directional refractive index of the prism is set as nx, its array-directional refractive index as ny and its thickness-directional refractive index as nz: when nxny, nz or nynx, nz, the crest of the prism is directed orthogonal to a transmission axis 6a of the polarizing plate 6; and when nynx, nz or nxny, nz, the crest of the prism is directed in parallel with the transmission axis 6a of the polarizing plate 6.
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Ori Akira
Yasuo Iisaka