Light guide plate, planer light source unit and reflection-type liquid-crystal display device

• US 6,199,995 B1
• Filed: 02/26/1999
• Issued: 03/13/2001
• Est. Priority Date: 02/26/1998
• Status: Expired due to Fees

• Current Assignee: Nitto Denko Corporation
• Original Assignee: Nitto Denko Corporation
• Inventors: Umemoto, Seiji, Yano, Shuji
• Primary Examiner(s): HUSAR, STEPHEN F
• Application Number:
  US09/258,256
• Time in Patent Office: 746 Days
• Field of Search: 362/261, 362/31, 362/27, 385/116
• US Class Current: 362/619
• 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 6/0046 Tapered light guide, e.g. wedge-shaped light guide
• CPC Class Codes: G02F 1/133616 Front illuminating devices

Abstract

A light guide plate in which the light incident on an entrance end surface is allowed to emerge from a bottom surface view a light issuing means formed on a top surface, with the direction of maximum intensity of the emerging light as measured in a plane perpendicular to the two reference planes defined by said entrance end surface and said bottom surface being within 30 degrees from the line normal to said bottom surface and wherein when the direction toward the entrance end surface away from said normal line taken as the reference is assumed to be negative, the intensity of the light leaking from the top surface at the same angle as the direction of said maximum intensity is no more than a tenth of said maximum intensity, with the incident light from the bottom surface being transmitted through the top surface; a planer light source unit having a light source adjacent the entrance end surface of the light guide plate; and a reflection-type liquid-crystal display device having a reflective layer furnished, liquid-crystal cell provided beneath the bottom surface of the planer light source unit.

Claims

1. A light guide plate comprising:

an entrance end surface on which light is incident;

a top surface having light issuing means; and

a bottom surface from which the light emerges via said light issuing means,

wherein, a direction of maximum intensity of the emerging light as measured in a plane perpendicular to two reference planes defined by said entrance end surface and said bottom surface is within 30 degrees from a line normal to said bottom surface, and

when a direction toward said entrance end surface away from the line normal to said bottom surface is assumed to be negative, intensity of light leaking form said top surface at the same angle as the direction of the maximum intensity is no more than a tenth of said maximum intensity, and

incident light from the bottom surface is transmitted through said top surface.

2. A light guide plate according to claim 1, wherein luminance of the emerging light from said bottom surface as measured in the direction of the normal line to said perpendicular plane is no more than 60% of luminance in the direction of said maximum intensity.

3. A light guide plate according to claim 1, wherein quantity of the light leaking at solid angles within 30 degrees with reference to the normal line is no more than ⅛

of quantity of the light emerging from said bottom surface.

4. A light guide plate according to claim 1, wherein said light issuing means comprises a repetition of prismatic asperities each having a shorter side plane and a longer side plane and being arranged on a pitch of 50 μ

m to 1.5 mm,

wherein said shorter side plane slopes downward from said entrance end surface to an opposed end to said entrance end surface at angles of inclination of 30 to 45 degrees with respect to the reference plane defined by said bottom surface,

wherein said longer side plane is inclined at angles in excess of zero degrees and up to 10 degrees with respect to the reference plane defined by said bottom surface, with the variation in the angle of inclination of all the longer side planes as measured throughout the light guide plate being within 5 degrees, and difference in the angle of inclination between one longer side plane and a nearest longer side plane being within 1 degree, and

wherein area of said longer side plane as projected onto the reference plane defined by said bottom surface is at least 5 times of projected area of said shorter side plane.

5. A light guide plate according to claim 4, wherein a width of each plane of the shorter side as projected onto the reference plane defined by said bottom surface is no more than 40 μ

m.

6. A light guide plate according to claim 4, wherein roundness of two vertexes in the prismatic asperities formed by said shorter side plane and two longer planes which are adjacent to said shorter plane is approximated by an arc of a circle, and sum of radii of the two arcs of a circle is no more than a half of a side length of said shorter side plane.

7. A light guide plate according to claim 4, wherein the prismatic asperities are arranged either parallel to or at an incline angle within ±

35 degrees with the reference plane defined by said entrance end surface.

8. A light guide plate according to claim 1, wherein normal incident light from said bottom surface passes through said top surface at a total ray transmission of at least 90% and with a haze of no more than 15%.

26. A light guide plate as set forth in claim 1, wherein said light issuing means comprises a repetition of prismatic asperities arranged on a pitch of 50 μ

m to ⅕

mm.

27. A light guide plate as set forth in claim 26, wherein a plane of said asperities slopes downward from said entrance end surface to an opposed end to said entrance end surface at angles of inclination of 30-45 degrees with respect to a reference plane defined by the bottom surface.

9. A planer light source unit comprising:

(A) a light guide plate comprising;

an entrance end surface on which light is incident;

a top surface having light issuing means; and

a bottom surface from which the light emerges via said light issuing means,

wherein, a direction of maximum intensity of the emerging light as measured in a plane perpendicular to two reference planes defined by said entrance end surface and said bottom surface is within 30 degrees from a line normal to said bottom surface,

when a direction toward said entrance end surface away from the line normal to said bottom surface is assumed to be negative, intensity of light leaking from said top surface at the same angle as the direction of the maximum intensity is no more than a tenth of said maximum intensity, and

incident light from the bottom surface is transmitted through said top surface; and

(B) a light source disposed adjacent to said entrance end surface.

10. A planer light source unit according to claim 9, wherein luminance of the emerging light from said bottom surface as measured in the direction of the normal line to said perpendicular plane is no more than 60% of luminance in the direction of said maximum intensity.

11. A planer light source unit according to claim 9, wherein quantity of the light leaking at solid angles within 30 degrees with reference to the normal line is no more than ⅛

of quantity of the light emerging from said bottom surface.

12. A planer light source unit according to claim 9, wherein said light issuing means comprises a repetition of prismatic asperities each having a shorter side plane and a longer side plane and being arranged on a pitch of 50 μ

m to 1.5 mm,

wherein said shorter side plane slopes downward from said entrance end surface to an opposed end to said entrance end surface at angles of inclination of 30 to 45 degrees with respect to the reference plane defined by said bottom surface,

wherein said longer side plane is inclined at angles in excess of zero degrees and up to 10 degrees with respect to the reference plane defined by said bottom surface, with the variation in the angle of inclination of all the longer side planes as measured throughout the light guide plate being within 5 degrees, and difference in the angle of inclination between one longer side plane and a nearest longer side plane being within 1 degree, and

wherein area of said longer side plane as projected onto the reference plane defined by said bottom surface is at least 5 times of projected area of said shorter side plane.

13. A planer light source unit according to claim 12, wherein a width of each plane of the shorter side as projected onto the reference plane defined by said bottom surface is no more than 40 μ

m.

14. A planer light source unit according to claim 12, wherein roundness of two vertexes in the prismatic asperities formed by said shorter side plane and two longer planes which are adjacent to said shorter plane is approximated by an arc of a circle, and sum of radii of the two arcs of a circle is no more than a half of a side length of said shorter side plane.

15. A planer light source unit according to claim 12, wherein the prismatic asperities are arranged either parallel to or at an incline angle within ±

35 degrees with the reference plane defined by said entrance end surface.

16. A planer light source unit according to claim 9, wherein normal incident light from said bottom surface passes through said top surface at a total ray transmission of at least 90% and with a haze of no more than 15%.

28. A light guide plate as set forth in claim 9, wherein said light issuing means comprises a repetition of prismatic asperities arranged on a pitch of 50 μ

m to ⅕

mm.

29. A light guide plate as set forth in claim 28, wherein a plane of said asperities slopes downward from said entrance end surface to an opposed end to said entrance end surface at angles of inclination of 30-45 degrees with respect to a reference plane defined by the bottom surface.

17. A reflection-type liquid-crystal display device comprising:

(A) a light guide plate comprising;

an entrance end surface on which light is incident;

a top surface having light issuing means; and

a bottom surface from which the light emerges via said light issuing means,

wherein, a direction of maximum intensity of the emerging light as measured in a plane perpendicular to two reference planes defined by said entrance end surface and said bottom surface is within 30 degrees from a line normal to said bottom surface,

when a direction toward said entrance end surface away from the line normal to said bottom surface is assumed to be negative, intensity of light leaking from said top surface at the same angle as the direction of the maximum intensity is no more than a tenth of said maximum intensity, and

incident light from the bottom surface is transmitted through said top surface;

(B) a light source disposed adjacent to said entrance end surface; and

(C) a reflective layer having a liquid-crystal cell and provided beneath said bottom surface.

18. A reflection-type liquid-crystal display device according to claim 17, wherein luminance of the emerging light from said bottom surface as measured in the direction of the normal line to said perpendicular plane is no more than 60% of luminance in the direction of said maximum intensity.

19. A reflection-type liquid-crystal display device according to claim 17, wherein quantity of the light leaking at solid angles within 30 degrees with reference to the normal line is no more than ⅛

of quantity of the light emerging from said bottom surface.

20. A reflection-type liquid-crystal display device according to claim 17, wherein said light issuing means comprises a repetition of prismatic asperities each having a shorter side plane and a longer side plane and being arranged on a pitch of 50 μ

m to 1.5 mm,

wherein said shorter side plane is an inclined surface which slopes downward from said entrance end surface to an opposed end to said entrance end surface at angles of inclination of 30 to 45 degrees with respect to the reference plane defined by said bottom surface,

wherein said longer side plane is inclined at angles in excess of zero degrees and up to 10 degrees with respect to the reference plane defined by said bottom surface, with the variation in the angle of inclination of all the longer side planes as measured throughout the light guide plate being within 5 degrees, and difference in the angle of inclination between one longer side plane and a nearest longer side plane being within 1 degree, and

wherein area of said longer side plane as projected onto the reference plane defined by said bottom surface is at least 5 times of projected area of said shorter side plane.

21. A reflection-type liquid-crystal display device according to claim 20, wherein a width of each plane of the shorter side as projected onto the reference plane defined by said bottom surface is no more than 40 μ

m.

22. A reflection-type liquid-crystal display device according to claim 20, wherein roundness of two vertexes in the prismatic asperities formed by said shorter side plane and two longer planes which are adjacent to said shorter plane is approximated by an arc of a circle, and sum of radii of the two arcs of a circle is no more than a half of a side length of said shorter side plane.

23. A reflection-type liquid-crystal display device according to claim 20, wherein the prismatic asperities are arranged either parallel to or at an incline angle within ±

35 degrees with the reference plane defined by said entrance end surface.

24. A reflection-type liquid-crystal display device according to claim 17, wherein normal incident light from said bottom surface passes through said top surface at a total ray transmission of at least 90% and with a haze of no more than 15%.

25. A reflection-type liquid-crystal display device according to claim 17, wherein said bottom surface of said light guide plate is brought into contact with a top surface of said liquid-crystal cell.

30. A light guide plate as set forth in claim 17, wherein said light issuing means comprises a repetition of prismatic asperities arranged on a pitch of 50 μ

m to ⅕

mm.

31. A light guide plate as set forth in claim 30, wherein a plane of said asperities slopes downward from said entrance end surface to an opposed end to said entrance end surface at angles of inclination of 30-45 degrees with respect to a reference plane defined by the bottom surface.