Lens sheet including lens with variable curvature and display device including the same
A lighting unit for a display device includes: a plurality of light sources which emits light; a wedge-shaped light guide having an incident surface disposed close to the light sources and an opposing surface disposed opposite the incident surface; and a lens sheet disposed on the light guide, where the lens sheet includes a plurality of lenses, each having an axis in a direction from the incident surface to the opposing surface, where the light guide is thinner at the incident surface than at the opposing surface, and a radius of curvature of each of the lenses is larger at the incident surface than the opposing surface.
1. A lighting unit for a display device comprising:
a plurality of light sources which emits light;
a wedge-shaped light guide having an incident surface disposed close to the light sources and an opposing surface disposed opposite the incident surface;
an optical sheet disposed on the light guide; and
a lens sheet disposed on the optical sheet and spaced apart from the light guide, wherein the lens sheet comprises a plurality of lenses, each having an axis in a direction from the incident surface to the opposing surface,
wherein,
the light guide is thinner in height at the incident surface than at the opposing surface,
a radius of curvature of each of the lenses adjacent to the incident surface is larger than the radius of curvature thereof adjacent to the opposing surface, and
the radius of curvature (R) of a portion of a lens of the lenses satisfies the following equation:
R =( n− 1)−[( a/M ) y +( b/M )],
wherein n denotes refractive index of the lens of the lenses, M denotes a magnification ratio of the lens, y denotes a position of the portion on the axis of the lens, and ‘a’ and ‘b’ denote constants determined based on a structure of the light guide, and
wherein a moving distance (H) of light from a corresponding light source of the light sources to the portion of the lens is given by ‘ay+b’.
2. The lighting unit of claim 1 , wherein the radius of curvature of each of the lenses becomes smaller from the incident surface to the opposing surface.
3. The lighting unit of claim 2 , wherein the radius of curvature of a portion of each of the lenses is substantially in proportion to a distance of the portion of each of the lenses from the opposing surface.
4. The lighting unit of claim 1 , wherein a light spreading angle (θ) satisfies the following equation:
θ
=
tan
-
1
1
x
H
-
D
(
n
-
1
)
2
R
-
tan
-
1
1
x
H
+
D
(
n
-
1
)
2
R
,
wherein D denotes a pitch of the lenses, and x denotes a distance from the corresponding light source in a direction substantially perpendicular to the axis of the lens on a surface substantially parallel to the lens sheet.
5. The lighting unit of claim 1 , wherein the light sources comprise three primary color light sources.
6. The lighting unit of claim 1 , wherein the light sources comprise a first light source group comprising:
a first-color light source; and
a plurality of second-color light sources arranged substantially symmetrically with respect to the first-color light source.
7. The lighting unit of claim 6 , wherein
the first-color light source comprises a green light source, and
the second-color light sources comprise two magenta light sources.
8. The lighting unit of claim 7 , wherein the light sources further comprise a white light source disposed closer to one of the two magenta light sources than the green light source.
9. The lighting unit of claim 7 , wherein
the light sources further comprise a second light source group comprising a red light source, a green light source and a blue light source, which are arranged in sequence, and
the second light source group is disposed in a middle portion of an arrangement of the light sources.
10. A display device comprising:
a plurality of light sources which emits light;
a wedge-shaped light guide having an incident surface disposed close to the light sources and an opposing surface disposed opposite the incident surface;
an optical sheet disposed on the light guide;
a lens sheet disposed on the optical sheet and spaced apart from the light guide, wherein the lens sheet comprises a plurality of lenses, each having an axis in a direction from the incident surface to the opposing surface; and
a display panel disposed on the lens sheet,
wherein
the light guide is thinner in height at the incident surface than at the opposing surface,
a radius of curvature of each of the lenses adjacent to the incident surface is larger than the radius of curvature thereof adjacent to the opposing surface, and
the radius of curvature (R) of a portion of a lens of the lenses satisfies the following equation,
R =( n− 1)×[( a/M ) y +( b/M )],
wherein n denotes refractive index of the lens of the lenses, M denotes a magnification ratio of the lens, y denotes a position of the portion on the axis of the lens, and ‘a’ and ‘b’ denote constants determined based on a structure of the light guide, and
wherein a moving distance (H) of light from a corresponding light source of the light sources to the portion of the lens is given by ‘ay+b’.
11. The display device of claim 10 , wherein the radius of curvature of each of the lenses becomes smaller from the incident surface to the opposing surface.
12. The display device of claim 11 , wherein the radius of curvature of a portion of each of the lenses is substantially in proportion to a distance of the portion thereof from the opposing surface.
13. The display device of claim 10 , wherein a light spreading angle (θ) satisfy the following equation:
θ
=
tan
-
1
1
x
H
-
D
(
n
-
1
)
2
R
-
tan
-
1
1
x
H
+
D
(
n
-
1
)
2
R
,
wherein D denotes a pitch of the lenses, and x denotes a distance from the corresponding light source in a direction substantially perpendicular to the axis of the lens on a surface substantially parallel to the lens sheet.
14. The display device of claim 10 , wherein the light sources comprise:
a first light source group comprising:
a green source; and
two magenta light sources arranged symmetrically with respect to the green light source.
15. The display device of claim 14 , wherein the light sources further comprise a white light source disposed closer to one of the magenta light sources than the green light source.
16. The display device of claim 14 , wherein the light sources further comprise:
a second light source group comprising a red light source, a green light source and a blue light source, which are arranged in sequence, and
the second light source group is disposed in a middle portion of an arrangement of the light sources.
17. The display device of claim 14 , wherein the display panel comprises:
a red pixel comprising a red color filter;
a blue pixel comprising a blue color filter; and
a green pixel disposed between the red pixel and the green pixel.