Patent ID: 8308314

Claim:
A direct-type surface light source system comprising: a first lenticular lens sheet having multiple unit lenses, each of the unit lenses projecting on the light-exiting side; a second lenticular lens sheet having multiple unit lenses, each of the unit lenses projecting on the light-exiting side; and a light source unit having emission sources, the emission sources being capable of being divided into two types or more according to wavelength ranges of light they emit, wherein the unit lenses in the first lenticular lens sheet are arranged in one direction parallel to a sheet plane of the first lenticular lens sheet at approximately regular intervals, wherein the unit lenses in the second lenticular lens sheet are arranged in other direction at approximately regular intervals, the other direction being parallel to a sheet plane of the second lenticular lens sheet and being perpendicular to the one direction, wherein the emission sources are arranged on a plane parallel to the sheet plane of the first lenticular lens sheet, wherein emission sources of each type are arranged in the one direction at approximately regular intervals, wherein intervals at which respective emission sources of two types or more arranged in the one direction are nearly the same in length, and wherein a length L of the intervals at which the emission sources of each type are arranged in the one direction, a distance d between the light source unit and the first lenticular lens sheet, measured along a normal to the sheet plane of the first lenticular lens sheet, an angle θ between the normal and a tangent line to an edge, in the one direction, of the unit lenses in a cross section taken along the one direction and along the normal, and a refractive index n of a material for the unit lenses fulfill the following relationship: cos −1 ( n ×cos(φ+θ))≦θ wherein φ=sin −1 (sin(tan −1 (L/2d))/n), or n ×cos(φ+θ)>1 wherein φ=sin −1 (sin(tan −1 (L/2d))/n).