Surface light source which selectively irradiates two linearly polarized light beams in polarized states different from each other and liquid crystal display apparatus using the same

• US 7,978,285 B2
• Filed: 03/19/2008
• Issued: 07/12/2011
• Est. Priority Date: 03/20/2007
• Status: Expired due to Fees

• Current Assignee: InterDigital Patent Holdings, Inc. (InterDigital, Inc.)
• Original Assignee: Casio Computer Company Limited
• Inventors: Daiku, Yasuhiro
• Primary Examiner(s): Nguyen; Hoan C
• Application Number:
  US12/077,512
• Publication Number:
  US 20080231773A1
• Time in Patent Office: 1,210 Days
• Field of Search: 349 62- 66, 362611-614, 345/87, 257/88
• US Class Current: 349/61
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• 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: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one
• CPC Class Codes: G02F 1/133631 with a spatial distribution of the retardation value
• CPC Class Codes: G02F 1/133638 Waveplates, i.e. plates with a retardation value of lambda/n
• CPC Class Codes: G09G 2310/063 Waveforms for resetting the whole screen at once
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 2320/0261 in the context of movement of objects on the screen or movement of the observer relative to the screen
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336

Abstract

A surface light source includes a light source which selectively irradiates two polarized light beams in polarized states different from each other, a light guide plate which includes a transparent plate having two plate surfaces facing each other and end faces surrounding the plate surfaces, and irradiates the two polarized light beams form an irradiation surface, and an optical element which irradiates irradiated light from the irradiation surface of the light guide plate toward a direction substantially normal to the light guide plate upon changing the propagation direction of the irradiated light. A liquid crystal display apparatus includes this surface light source, a polarization control element which is placed on the observation side of the surface light source and rotates the polarization plane of linearly polarized light transmitted through one of partitioned first and second areas through a predetermined angle, and a liquid crystal display device placed on the observation side.

Claims

1. A surface light source comprising:

a light source which selectively irradiates two polarized light beams in polarized states different from each other;

a light guide plate comprising a transparent plate having two plate surfaces facing each other, the light guide plate guiding two light beams selectively irradiated from the light source into the transparent plate upon allowing the light to enter from an end face of the light guide plate, and irradiating the light from an irradiation surface which comprises one of the two plate surfaces; and

an optical element which irradiates irradiated light from the irradiation surface of the light guide plate in a direction substantially normal to the light guide plate upon changing a propagation direction of the irradiated light;

wherein the light source comprises;

a first light-emitting element and a second light-emitting element which are arranged on the end face of the light guide plate so as to face each other;

a first polarizing element which is provided between the first light-emitting element and the end face of the light guide plate and has a transmission axis in a direction substantially perpendicular to the irradiation surface of the light guide plate; and

a second polarizing element which is provided between the second light-emitting element and the end face of the light guide plate and has a transmission axis in a direction substantially parallel to the irradiation surface of the light guide plate.

2. The surface light source according to claim 1, wherein the light source comprises a first light source unit including the first light-emitting element and the first polarizing element and a second light source unit including the second light-emitting element and the second polarizing element, said first and second light source units being arranged on the end face of the light guide plate so as to face each other.

3. The surface light source according to claim 2, further comprising a light-shielding plate provided between the first light source unit and the second light source unit which are alternately arranged on the end face of the light guide plate.

4. The surface light source according to claim 1, wherein the light guide plate comprises a reflecting member on a side of the other of the two plate surfaces which faces the irradiation surface.

5. The surface light source according to claim 1, wherein the optical element comprises a prism sheet comprising densely arranged elongated minute prisms extending in a direction substantially parallel to the end face of the light guide plate on which the light source is arranged.

6. A liquid crystal display apparatus comprising:

a surface light source which selectively applies first illumination light comprising first linearly polarized light having a polarization plane in a predetermined direction and second illumination light comprising linearly polarized light having a polarization plane substantially perpendicular to the polarization plane of the first linearly polarized light;

a polarization control element provided on a surface side of the surface light source from which illumination light is irradiated, wherein the polarization control element has an area which corresponds to an illumination light irradiation surface of the surface light source and is partitioned into a first area corresponding to a predetermined range and a second area other than the first area, and rotates a polarization plane of linearly polarized light transmitted through one of the partitioned first and second areas by a predetermined angle;

a liquid crystal display device comprising a polarizing plate which is provided on a light irradiation surface side of the polarization control element so as to correspond to both the first and second areas and which has a transmission axis substantially parallel to a polarization plane of linearly polarized light irradiated to the irradiation surface side upon being transmitted through one of the first and second areas of the polarization control element, wherein the liquid crystal display device comprises a screen area in which pixels which control transmission of light are arrayed in row directions and column directions, and wherein the liquid crystal display device displays, in the screen area, an image corresponding to image data supplied to the pixels; and

a driving unit which, in one frame for display a one-frame image, causes the surface light source to apply one of the first illumination light and the second illumination light in a period during which the image data are supplied to pixels on each row corresponding to the first area of the polarization control element, and causes the surface light source to apply the other of the first illumination light and the second illumination light in a period during which the image data are supplied to pixels on each row corresponding to the second area of the polarization control element.

7. The liquid crystal display apparatus according to claim 6, wherein the surface light source comprises:

a light guide plate comprising a transparent plate having two plate surfaces facing each other, the light guide plate guiding the selectively applied first illumination light and second illumination light into the transparent plate upon allowing the light to enter from an end face of the light guide plate, and irradiating the light from an irradiation surface which comprises one of the two plate surfaces;

a first light-emitting element and a second light-emitting element which are arranged on the end face of the light guide plate so as to face each other and which irradiate the first illumination light and the second illumination light, respectively;

a first polarizing element which is provided between the first light-emitting element and the end face of the light guide plate and has a transmission axis in a direction substantially perpendicular to the irradiation surface of the light guide plate;

a second polarizing element which is provided between the second light-emitting element and the end face of the light guide plate and has a transmission axis in a direction substantially parallel to the irradiation surface of the light guide plate; and

an optical element which irradiates irradiated light from the irradiation surface of the light guide plate in a direction substantially normal to the light guide plate upon changing a propagation direction of the irradiated light.

8. The liquid crystal display apparatus according to claim 7, wherein a first light source unit comprising the first light-emitting element and the first polarizing element and a second light source unit comprising the second light-emitting element and the second polarizing element are arranged on the end face of the light guide plate so as to face each other.

9. The liquid crystal display apparatus according to claim 6, wherein the polarization control element comprises a λ

/2 retardation film which is provided in an area corresponding to one of the first and second areas and rotates a polarization plane of one of the first illumination light and the second illumination light comprising linearly polarized light irradiated from the surface light source.

10. The liquid crystal display apparatus according to claim 9, wherein the λ

/2 retardation film is placed so that a slow axis thereof is in a direction intersecting the polarization planes of the first illumination light and the second illumination light from the surface light source at an angle of substantially 45°

.

11. The liquid crystal display apparatus according to claim 6, wherein the polarization control element is partitioned into a first area corresponding to pixel rows of the liquid crystal display device, and a second area corresponding to rows other than the pixel rows corresponding to the first area.

12. The liquid crystal display apparatus according to claim 6, wherein the liquid crystal display device comprises a liquid crystal panel including a pair of substrates and a liquid crystal layer sealed between the substrates, and a pair of polarizing plates provided on both sides of the liquid crystal panel with transmission axes of the polarizing plates being substantially perpendicular to each other.

13. The liquid crystal display apparatus according to claim 6, wherein:

the polarization control element is partitioned into a first area corresponding to rows consecutive in a direction in which pixel rows of the liquid crystal display device are sequentially scanned, and a second area corresponding to other rows to be scanned following pixel rows corresponding to the first area, and

the driving unit comprises a driving circuit which drives the surface light source and the liquid crystal display device to (i) sequentially scan rows corresponding to the first area and rows corresponding to the second area so as to supply image data to pixels on each row, for each frame for displaying a one-frame image, (ii) cause the surface light source to apply one of the first illumination light and the second illumination light in a period during which the image data are supplied to pixels on each row corresponding to the first area, and (iii) cause the surface light source to apply the other of the first illumination light and the second illumination light in a period during which the image data are supplied to pixels on each row corresponding to the second area.

14. The liquid crystal display apparatus according to claim 13, wherein:

the polarization control element is partitioned into a first area and a second area by substantially equally dividing the number of pixel rows by two in a direction in which pixel rows of the liquid crystal display device are scanned, and

the driving circuit supplies the image data to pixels on each row corresponding to the first area while causing the surface light source to apply one of the first illumination light and the second illumination light in a first half period of periods obtained by substantially equally dividing one frame by two, and supplies the image data to pixels on each row corresponding to the second area while causing the surface light source to apply the other of the first illumination light and the second illumination light in a second half period of the one frame.