ILLUMINATING DEVICE AND LIQUID CRYSTAL DISPLAY DEVICE

• US 20110221998A1
• Filed: 02/17/2011
• Published: 09/15/2011
• Est. Priority Date: 03/12/2010
• Status: Active Grant

• Current Assignee: Panasonic Intellectual Property Corporation of America (Panasonic Holdings Corporation)
• Original Assignee: Hitachi Displays Limited (Japan Display Incorporated)
• Inventors: Adachi, Masaya, Sugita, Tatsuya
• Granted Patent: US 9,829,622 B2
• Time in Patent Office: Days
• US Class Current: 349/62
• CPC Class Codes: G02B 6/0036 2-D arrangement of prisms, protrusions, indentations or roughened surfaces
• CPC Class Codes: G02B 6/0038 Linear indentations or grooves, e.g. arc-shaped grooves or meandering grooves, extending over the full length or width of the light guide
• CPC Class Codes: G02B 6/0056 for producing polarisation effects, e.g. by a surface with polarizing properties or by an additional polarizing elements
• CPC Class Codes: G02B 6/0068 Arrangements of plural sources, e.g. multi-colour light sources
• CPC Class Codes: G02B 6/0073 Light emitting diode [LED]
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side

Abstract

An illuminating device includes: a light source; a light guide plate which converts light emitted from the light source into a surface light ray and emits the surface light ray through a front surface of the light guide plate; and an optical sheet which changes a propagation direction of the surface light ray emitted from the light guide plate. The light source is arranged in end surface different from the front surface in the light guide plate. A polarization state converting structure to convert a polarization state of the light propagating through the light guide plate is provided in a surface opposing the front surface in the light guide plate. The polarization state converting structure contains an inclination plane having a ridge line in a direction different from a direction in parallel to the longitudinal direction of the end surface.

Claims

1. An illuminating device comprising:

a light source;

a light guide plate which converts light emitted from the light source into a surface light ray and emits the surface light ray through a front surface of the light guide plate; and

an optical sheet which changes a propagation direction of the surface light ray emitted from the light guide plate,

wherein the light source is arranged in one end surface different from the front surface in the light guide plate,

wherein the light guide plate has birefringence in at least an in-plane direction of the front surface and is formed of a transparent medium having a slow axis in parallel to a longitudinal direction of the end surface,

wherein a polarization state converting structure to convert a polarization state of the light propagating through the light guide plate is provided in a surface opposing the front surface in the light guide plate, and

wherein the polarization state converting structure includes an inclination plane having a ridge line in a direction different from a direction in parallel to the longitudinal direction of the end surface.

4. The illuminating device according to claim 1,

wherein the polarization state converting structure has the ridge line in a direction perpendicular to the longitudinal direction of the end surface.

5. The illuminating device according to claim 1,

wherein the polarization state converting structure includes a V-like structure having the ridge line in a direction different from a direction in parallel to the longitudinal direction of the end surface.

6. The illuminating device according to claim 5,

wherein the V-like structure in the polarization state converting structure has an apex angle which falls within a range of 80°

to 130°

.

7. The illuminating device according to claim 1,

wherein the inclination plane in the polarization state converting structure has an inclination angle to the front surface, which falls within a range of 40°

to 65°

.

8. The illuminating device according to claim 1,

wherein the optical sheet includes a base material and a prism array containing a plurality of prisms which are provided in a surface of the base material facing the light guide plate or a different surface opposing the surface of the base material facing the light guide plate,

wherein each of the prisms has at least two inclination planes and a ridge line of the prism is in parallel to the longitudinal direction of the end surface in the light guide plate, and

wherein the base material includes a transparent medium which produces no phase difference for p-polarized light emitted from the light guide plate and incident into the base material at a predetermined incident angle.

9. The illuminating device according to claim 8,

wherein the transparent medium included in the base material has birefringence in an in-plane direction in which the prism array is provided, and a slow axis of the transparent medium is in parallel or perpendicular to a ridge line direction of the prisms.

10. The illuminating device according to claim 8,

wherein the transparent medium included in the base material has biaxial anisotropy and a slow axis of the transparent medium is in parallel or perpendicular to a ridge line direction of the prisms.

11. The illuminating device according to claim 1,

wherein the optical sheet includes a base material, a prism array containing a plurality of prisms provided in a surface of the base material opposing the light guide plate, and an s-polarized light high reflecting layer provided in a surface of the base material facing the light guide plate,

wherein each of the prisms has at least two inclination planes and a ridge line of the prism is in parallel to the longitudinal direction of the end surface in the light guide plate,

wherein the base material includes a transparent medium which produces no phase difference for p-polarized light emitted from the light guide plate and incident into the base material at a predetermined incident angle, and

wherein the s-polarized light high reflecting layer includes a transparent medium which reflects an s-polarized light component of light emitted from the light guide plate and incident into the s-polarized light high reflecting layer at a predetermined incident angle in order to increase a percentage of p-polarized light component in light transmitted through the optical sheet.

12. The illuminating device according to claim 11,

wherein the s-polarized light high reflecting layer has a thickness varying depending on a predetermined angle and contains a layer made of a transparent material having a refractive index higher than the refractive index of the base material in the optical sheet.

13. A liquid crystal display device comprising:

an illuminating device according to claim 1; and

a liquid crystal display panel which is arranged in the propagation direction of the surface light ray emitted from the illuminating device,

wherein the liquid crystal display panel includes a pair of polarizers arranged with a liquid crystal layer interposed between the pair of polarizers, and

wherein a direction of an absorption axis of the polarizer arranged closer to the illuminating device, of the pair of polarizers, is set such that an angle formed with the longitudinal direction of the end surface of the light guide plate is smaller than an angle formed with a direction perpendicular to the longitudinal direction of the end surface of the light guide plate.

2. An illuminating device comprising:

a light source;

a light guide plate which converts light emitted from the light source into a surface light ray and emits the surface light ray through a front surface of the light guide plate;

a high refractive index layer formed on the front surface of the light guide plate; and

an optical sheet which changes a propagation direction of the surface light ray emitted from the light guide plate,

wherein the light source is arranged in one end surface different from the front surface in the light guide plate,

wherein the high refractive index layer has a refractive index higher than a refractive index of the light guide plate,

wherein a polarization state converting structure to convert a polarization state of the light propagating through the light guide plate is provided in a surface opposing the front surface in the light guide plate, and

wherein the polarization state converting structure includes an inclination plane having a ridge line in a direction different from a direction in parallel to the longitudinal direction of the end surface.

3. The illuminating device according to claim 2,

wherein, assuming that a thickness of the high refractive index layer is d_h, the refractive index of the high refractive index layer is n_h, and an angle at which light emitted at an angle providing the maximum luminance or luminous intensity in the surface light ray emitted from the light guide plate passes through the high refractive index layer is ξ

,

a relationship between the thickness d_h, the refractive index n_h and the angle ξ

for light having a visible wavelength λ

satisfies the following equation.

d_h≅

λ

/(4·

n_h·

cos ξ

)

14. The illuminating device according to claim 2,

wherein the polarization state converting structure has the ridge line in a direction perpendicular to the longitudinal direction of the end surface.

15. The illuminating device according to claim 2,

wherein the polarization state converting structure includes a V-like structure having the ridge line in a direction different from a direction in parallel to the longitudinal direction of the end surface.

16. The illuminating device according to claim 2,

wherein the inclination plane in the polarization state converting structure has an inclination angle to the front surface, which falls within a range of 40°

to 65°

.

17. The illuminating device according to claim 2,

wherein the optical sheet includes a base material and a prism array containing a plurality of prisms which are provided in a surface of the base material facing the light guide plate or a different surface opposing the surface of the base material facing the light guide plate,

wherein each of the prisms has at least two inclination planes and a ridge line of the prism is in parallel to the longitudinal direction of the end surface in the light guide plate, and

wherein the base material includes a transparent medium which produces no phase difference for p-polarized light emitted from the light guide plate and incident into the base material at a predetermined incident angle.

18. The illuminating device according to claim 15,

wherein the V-like structure in the polarization state converting structure has an apex angle which falls within a range of 80°

to 130°

.

19. The illuminating device according to claim 17,

wherein the transparent medium included in the base material has birefringence in an in-plane direction in which the prism array is provided, and a slow axis of the transparent medium is in parallel or perpendicular to a ridge line direction of the prisms.

20. A liquid crystal display device comprising:

an illuminating device according to claim 2; and

a liquid crystal display panel which is arranged in the propagation direction of the surface light ray emitted from the illuminating device,

wherein the liquid crystal display panel includes a pair of polarizers arranged with a fluid crystal layer interposed between the pair of polarizers, and

wherein a direction of an absorption axis of the polarizer arranged closer to the illuminating device, of the pair of polarizers, is set such that an angle formed with the longitudinal direction of the end surface of the light guide plate of the illuminating device is smaller than an angle formed with a direction perpendicular to the longitudinal direction of the end surface of the light guide plate of the illuminating device.

21. The illuminating device according to claim 2,

wherein the optical sheet includes a base material and a prism array containing a plurality of prisms which are provided in a surface of the base material facing the light guide plate or a different surface opposing the surface of the base material facing the light guide plate,

wherein each of the prisms has at least two inclination planes and a ridge line of the prism is in parallel to the longitudinal direction of the end surface in the light guide plate, and

wherein the base material includes a transparent medium which produces no phase difference for p-polarized light emitted from the light guide plate and incident into the base material at a predetermined incident angle.