Liquid crystal panel module with polarization transformation for increased brightness

• US 6,147,725 A
• Filed: 10/20/1998
• Issued: 11/14/2000
• Est. Priority Date: 11/21/1997
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Yuuki, Akimasa, Sasagawa, Tomohiro
• Primary Examiner(s): Dudek, James A.
• Assistant Examiner(s): CHOWDHURY, TARIFUR RASHID
• Application Number:
  US09/175,542
• Time in Patent Office: 756 Days
• Field of Search: 349/61, 349/62, 349/65, 349/96, 385/146, 362/32
• US Class Current: 349/65
• 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

Abstract

A liquid crystal panel module includes a backlight unit consisting of a light guide plate having a reflecting sheet at a lower face, a lamp for projecting light to one side of the light guide plate, a reflector for condensing the light from the lamp onto the light guide plate, and a liquid crystal panel having a polarizing plate at a lower face and disposed on the backlight unit. Equilateral prisms are located between the light guide plate and reflecting sheet of the backlight unit in a direction parallel to a polarization axis of the polarizing plate of the liquid crystal panel unit. Each of the prisms has a prism angle so that the angle of incidence of the light guided from the lamp into the light guide plate is the Brewster angle of the prisms.

Claims

1. A liquid crystal panel module comprising:

a backlight unit including

a light guide plate having a first index of refraction, a front surface, a back surface including a plurality of grooves and located opposite the front surface, and a side surface transverse to the front and rear surfaces,

a reflecting sheet at the back surface of said light guide plate,

a lamp for illuminating the side surface of said light guide plate, and

a reflector condensing light radiated from said lamp onto the side surface of said light guide plate;

a liquid crystal panel unit arranged opposite the front surface of said light guide plate of said backlight unit and including a polarizing plate having a polarization axis and located on a rear surface of said liquid crystal panel unit opposite the front surface of said light guide plate; and

a plurality of equilateral prisms arranged within and filling the grooves in said light guide plate, exposed at the back surface of said light guide plate, and arranged in a direction parallel to the polarization axis of said polarizing plate, each of said plurality of equilateral prisms having a prism angle so that light guided into said light guide plate impinges on a surface of an equilateral prism at the Brewster angle of said equilateral prism, said equilateral prisms having a second index of refraction larger than the first index of refraction of said light guide plate.

2. The liquid crystal panel module according to claim 1 further comprising a polarization rotating plate at the back surface of said facing said light guide plate, between said reflecting sheet and said light guide plate, for rotating polarization direction of incident light.

3. A liquid crystal panel module comprising:

a backlight unit including

a light guide plate having a first index of refraction, a front surface, a back surface including a plurality of grooves and located opposite the front surface, and a side surface transverse to the front and back surfaces,

a reflecting sheet on the back surface of said light guide plate,

a lamp for illuminating the side surface of said light guide plate,

a polarizing separating film disposed on the side surface of said light guide plate, between said lamp and said light guide plate, and

a reflector condensing light radiated from said lamp onto the side surface of said light guide plate through said polarizing separating film;

a liquid crystal panel unit arranged opposite the front surface of said light guide plate of said backlight unit and including a polarizing plate having a polarization axis and located on a rear surface of said liquid crystal panel unit opposite the front surface of said light guide plate wherein said polarizing separating film has a polarization direction aligned with the polarization axis of said polarizing plate; and

a plurality of reflecting members arranged within and filling the grooves in said light guide plate and exposed at the back surface of said light guide plate, reflecting light guided into said light guide plate directly into said liquid crystal panel unit, wherein said plurality of reflecting members have a second index of refraction larger than that of the first index of refraction of said light guide plate.

4. The liquid crystal panel module according to claim 3 wherein said plurality of reflecting members comprise a plurality of equilateral prisms, each of said plurality of equilateral prisms having a prism angle so that light guided into said light guide plate impinges on a surface of an equilateral prism at the Brewster angle of said equilateral prism.

5. The liquid crystal panel module according to claim 3 wherein said plurality of reflecting members comprises a plurality of right angle prisms.

6. A liquid crystal panel module comprising:

a backlight unit including

a hollow light guide having a front wall and a side wall transverse to the front wall, together partially defining a hollow volume,

a reflecting sheet at a back wall of said hollow light guide,

a lamp for illuminating said hollow light guide at an open side of said hollow light guide, opposite the side wall,

a polarization rotating plate on said reflecting sheet facing said front wall, forming the back wall and partially defining the hollow volume, for rotating polarization direction of light incident at an angle on said polarization rotating plate, and

a reflector condensing light radiated from said lamp into said hollow light guide;

a liquid crystal panel unit arranged opposite the front wall of said hollow light guide of said backlight unit and including a polarizing plate having a polarization axis located on a rear surface of said liquid crystal panel unit opposite the front wall of said hollow light guide; and

a plurality of equilateral prisms arranged within said hollow light guide at said polarization rotating plate, in a direction parallel to the polarization axis of said polarizing plate, each of said plurality of equilateral prisms having a prism angle so that light guided into said hollow light guide impinges on a surface of an equilateral prism at the Brewster angle of said equilateral prism wherein said equilateral prisms have an index of refraction larger than in the hollow volume of said hollow light guide.

7. The liquid crystal panel module according to claim 6 further comprising a polarization rotating plate at the back wall of said hollow light guide, between said reflecting sheet and said hollow light guide, for rotating polarization direction of incident light.