| 摘要 |
<p>A directly downward type backlight device comprising, arranged in this order, a reflection plate, a plurality of linear light sources arranged in parallel and a light diffusion plate, wherein the light diffusion plate has on at least one main plane thereof a plurality of recessed or protruding structure units each having at least three inclined side surfaces with the maximum height Rz of a main plane having structure units being up to 1,000 µm, and a portion, having the relation 12.5-10×(b<SUB>L</SUB>/a<SUB>L</SUB>)<XN<85-25×(B<SUB>L</SUB>/a<SUB>L</SUB>) between, an average distance a<SUB>L</SUB> (mm) between the center axes of linear light sources that have at least two lines representing inclined side surfaces n having different inclinations Xn (unit:degree, n is natural number and a sub-index representing each inclined side surface.) with all the inclinations Xn being adjacent to each other, and the minimum distance b<SUB>L</SUB> (mm) between the center axis of a linear light source and the main plane on the linear light source side of the light diffusion plate, is included in the vertical section of the light diffusion plate having a cutting line in a direction perpendicular to the center axis direction of a linear light source in a region directly above the region between the center axis of adjacent linear light sources.</p> |
