Patent ID: 8659840

Claim:
An optical element, comprising: a first optical sheet having a first major surface, the first optical sheet including a first Fresnel lens provided in the first major surface, the first Fresnel lens including a plurality of ridge portions having concentric circular configurations, widths of mutually adjacent ridge portions of the plurality of ridge portions along a radial direction from a center of the concentric circles toward the outside being different from each other, the width along the radial direction of each of the plurality of ridge portions being not more than 0.43 millimeters, wherein a difference of the widths of the mutually adjacent ridge portions of the plurality of ridge portions is not less than 0.050 millimeters, the plurality of ridge portions includes: a first ridge portion having a first width along the radial direction; a second ridge portion adjacent to the first ridge portion and provided outside the first ridge portion, the second ridge portion having a second width along the radial direction, the second width being larger than the first width; and a third ridge portion adjacent to the second ridge portion and provided outside the second ridge portion, the third ridge portion having a third width along the radial direction, the third width being smaller than the first width, the first to third ridge portions are provided repeatedly.