Patent ID: 11886075
Assignee: KEIWA INCORPORATED
Field: Optics (Instruments)
Classification: CPC G  F | IPC G

Claim 10:
11. A method for evaluating an optical sheet to be interposed between a plurality of small light sources and a prism sheet in a liquid crystal display device having the small light sources arranged in a dispersed manner at a side of the liquid display device opposite to a display screen, wherein:
at least one surface of the optical sheet has unevenness having recesses, each recess having an inverted pyramid shape and being two-dimensionally arrayed,
a distance between the plurality of small light sources and the optical sheet is 2 mm or less, and
a ratio of: (I) a total area of some of minute regions, which have surfaces inclined at inclination angles of 30° or more from an imaginary plane that is a flat surface appearing after imaginarily removing the unevenness; with respect to (II) a total area of all the minute regions is calculated, for which the inclination angles are obtained by approximating the surfaces of the minute regions with the unevenness to flat surfaces, while two-dimensionally shifting the minute region with a projection area of 10 μm2 or less and a square shape with respect to the imaginary plane at equal intervals along the imaginary plane to obtain the minute regions at respective points on the imaginary plane.