| 摘要 |
PURPOSE: To make a back light have an excellent directivity with which the luminous intensity on a front surface is made highest, to simplify the structure of the back light and to make the structure compact by using the light guiding body having a specific structure as a light guiding body. CONSTITUTION: This back light is constituted of a light source is and the plate shaped light guiding body 2 having at least one light incident surface opposite to the light source 1 and a light emission surface and many projection shaped prism strings 7 having prism surfaces whose inclination angles with respect to the light emission surface are in the range ofϕ±5 degrees (ϕis expressed as≃=45 deg.-(COS<-1> ((nd /nr ) COSθC)+COS<-1> (nd /nr ))/4) are formed parallel with respect to the light incident surface on the rear surface opposed to the light emission surface of the guiding body 2. That is, this back light is consisting of the light source 1 and the light guiding body 2 and the light source 1 is arranged on the surface of the thickness direction of the light guiding body 2. The light guiding body 2 is constituted of a plate shaped body whose side surface is made to be the light incident surface and in which the surface orthogonal to the light incident surface is made to be the light emission surface and many projection shaped prism strings 7 are formed parallel with respect to the light incident surface on the rear surface opposed to the light emission surface.
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