Backlight unit and liquid crystal display device

1. A backlight unit comprising:

a light-source substrate having mounted thereon a plurality of light-emitting elements that emit illumination light;

a light guide plate having a side surface with the light-source substrate attached thereto so as to receive the illumination light from the light-emitting elements, the light guide plate also having a first surface extending substantially perpendicular to the side surface, and a second surface, wherein the light guide plate has a thickness extending between the first and second surfaces;

a reflective sheet attached to the first surface of the light guide plate so as to reflect the illumination light from the light-emitting elements towards the second surface of the light guide plate; and

an optical sheet layer attached to the second surface of the light guide plate and comprising a plurality of optical sheets in a stacked manner,

wherein the side surface of the light guide plate to which the light-source substrate is attached is provided with a reflective portion that reflects illumination light received by the light guide plate from the light-emitting elements,

wherein the light guide plate is shaped such that substantially all of the illumination light received by the reflective portion from the light-emitting elements is incident on the reflective portion at an incidence angle that is equal to or above a critical angle, such that the illumination light received by the reflective portion is reflected within the light guide plate;

wherein the thickness of the light guide plate is gradually reduced approaching the side surface; and

wherein a first thickness of the light guide plate at the side surface is smaller than a second thickness of the light guide plate at a central region of the light guide plate outside the reflective portion, wherein the reflective portion at the side surface of the light guide plate has a stepped profile.

2. The backlight unit according to claim 1 , wherein the reflective portion of the light guide plate has a curved surface or a flat surface.

3. The backlight unit according to claim 1 , wherein the light-source substrate is attached to the side surface of the light guide plate in a manner such that the light-emitting elements mounted on the light-source substrate are accommodated in the light guide plate.

4. The backlight unit according to claim 1 , wherein the light guide plate contains a transparent resin material.

5. The backlight unit according to claim 1 , wherein the reflective portion at the side surface of the light guide plate is provided with a reflective member having a specular reflection function.

6. The backlight unit according to claim 1 , wherein the light-emitting elements and the light guide plate have optically transparent resin filled therebetween.

7. A liquid crystal display device comprising:

a transmissive liquid crystal panel; and

a backlight unit that illuminates the transmissive liquid crystal panel from a rear side of the panel,

wherein the backlight unit comprises:

a light-source substrate having mounted thereon a plurality of light-emitting elements that emit illumination light,

a light guide plate having a side surface with the light-source substrate attached thereto so as to receive the illumination light from the light-emitting elements, the light guide plate also having a first surface extending substantially perpendicular to the side surface, and a second surface, wherein the light guide plate has a thickness extending between the first and second surfaces,

a reflective sheet attached to the first surface of the light guide plate so as to reflect the illumination light from the light-emitting elements towards the second surface of the light guide plate, and

an optical sheet layer attached to the second surface of the light guide plate and comprising a plurality of optical sheets in a stacked manner,

wherein the side surface of the light guide plate to which the light-source substrate is attached is provided with a reflective portion that reflects at least some of the illumination light received by the light guide plate from the light-emitting elements,

wherein the light guide plate is shaped such that substantially all of the illumination light received by the reflective portion from the light-emitting elements is incident on the reflective portion at an incidence angle that is equal to or above a critical angle, such that the illumination light received by the reflective portion is reflected within the light guide plate;

wherein the thickness of the light guide plate is gradually reduced approaching the side surface; and

wherein a first thickness of the light guide plate at the side surface is smaller than a second thickness of the light guide plate at a central region of the light guide plate outside the reflective portion, wherein the reflective portion at the side surface of the light guide plate has a stepped profile.

8. The liquid crystal display device according to claim 7 , wherein the reflective portion of the light guide plate has a curved surface or a flat surface.

9. The liquid crystal display device according to claim 7 , wherein the light-source substrate is attached to the side surface of the light guide plate in a manner such that the light-emitting elements mounted on the light-source substrate are accommodated in the light guide plate.

10. The liquid crystal display device according to claim 7 , wherein the light guide plate contains a transparent resin material.

11. The liquid crystal display device according to claim 7 , wherein the reflective portion at the side surface of the light guide plate is provided with a reflective member having a specular reflection function.

12. The liquid crystal display device according to claim 7 , wherein the light-emitting elements and the light guide plate have optically transparent resin filled therebetween.