Lighting device and light control member used therefor and image display device using the lighting device and the light control member

A lighting device comprising:

• a rectangular emission surface formed of a X direction and a Y direction, the Y direction being vertical to the X direction;
• and
• a reflective plate, a plurality of linear light sources and a plate shape light control member,
• wherein the reflective plate is placed in parallel to the X direction and the Y direction,
• the linear light sources are placed in one virtual flat surface, the virtual flat surface being in parallel to the X direction and the Y direction by the emission surface side of the reflective plate,
• the linear light sources in a longitudinal direction are parallel to the Y direction and also arranged at a regular interval along the X direction,
• the light control member is placed by the emission surface side of the arranged linear light sources and a principal surface is parallel to the virtual flat surface where the linear light sources are arranged,
• the principal surface of the light control member is formed of an incident surface opposite to the linear light sources for receiving light from the linear light sources and an emission surface for outputting light received to the incident surface,
• the emission surface has a plurality of ridge form convex portions to a surface thereof,
• a ridge form ridgeline of a top part of the convex portions is formed in parallel to the Y direction and also arranged along the X direction,
• with a distance between centers of the linear light sources being D, a distance between a center of any of the linear light sources and the light control member being H and a function representing an outgoing light intensity of light entered from one linear light source to the light control member to a normal direction of the emission surface at a position coordinate X (light source position shall be X=0) in the X direction being f(X),
• with g(X)=f(X−D)+f(X)+f(X+D) (1),
• in a range of −D/2≦X≦D/2, a ratio g(X)min/g(X)max between g(X)min and g(X)max is 0.6 or more, g(X)min being the minimum value of g(X) and g(X)max being the maximum value of g(X),
• Xmin, a minimum value of X, is in a range of −3.0D≦Xmin≦−0.5D, Xmax, a maximum value of X, is in a range of 0.5≦Xmax≦3.0D (where Xmin and Xmax are coordinates of both ends when a value of f(X) declines centering near one linear light source in which the value of f(X) is X=0 and becomes practically 0), and
• a cross-sectional shape of a given convex portion in the X direction is formed of areas −N to N with (2N+1) number of different gradients represented by following formulas:
• δ=(Xmax−Xmin)/(2N+1) (2)
• Xi=i×δ (3)
• αi=Tan−1(Xi/H) (4)
• βi=Sin−1((1/n)sin αi) (5)
• γi=Sin−1((1/n2)sin αi) (6)
• ai∝f(Xi+T·tan γi)·cos Φi·cos βi/cos αi/cos(Φi−βi) (7)
• Φi=Tan−1((n·sin βi)/(n·cos βi−1)) (8)
• where
• N:
• Natural number
• i:
• Integer from −N to N
• n:
• Refractive index of a convex portion of the light control member
• n2:
• Refractive index of a base material of the light control member
• ai:
• Width of an area i in the X direction
• Φi:
• A gradient of a slope to an emission surface of the area i
• T:
• Thickness from the incident surface to a bottom part of a convex portion of the light control member.