Prismatic Film Backlight

• US 20100014312A1
• Filed: 10/10/2007
• Published: 01/21/2010
• Est. Priority Date: 10/10/2006
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Travis, Adrian
• Granted Patent: US 8,016,475 B2
• Time in Patent Office: Days
• US Class Current: 362/606
• CPC Class Codes: G02B 5/045 Prism arrays
• CPC Class Codes: G02B 6/0031 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0046 Tapered light guide, e.g. wedge-shaped light guide
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer

Abstract

A selectively light-reflecting sheet (30) includes a prismatic film (1) with parallel prisms (10) on its face, a low-index film (3) on the prisms and a layer (5) on the low-index film, this layer having a substantially flat surface. This results in a low effective index, which means that light incident at steeper angles on the prismatic film (1) will pass through it. This “leaky” effect can be used in conjunction with a reflector sheet (20) in a tapered-waveguide arrangement to construct a lightweight backlight.

Claims

1. A selectively light-reflecting sheet comprising:

a prismatic film with parallel prisms on its face,

a low-index film on the prisms and

a cover layer on the low-index film, this layer having a substantially flat surface.

2. A sheet according to claim 1, in which the thickness of the low-index layer is about 10 μ

m.

3. A sheet according to claim 1, in which the prismatic film and the cover layer have a refractive index of about 1.5, and the intermediate layer of about 1.2-1.3.

4. A sheet according to claim 1, in which the prismatic film and cover layer are made of plastics, such as polycarbonate or acrylic materials.

5. A light guide comprising:

a sheet comprising;

a prismatic film with parallel prisms on its face;

a low-index film on the prisms; and

a cover layer on the low-index film, this layer having a substantially flat surface; and

further including a reflective layer facing the prismatic film.

6. A light guide according to claim 5, wherein the sheet is at a slight angle to the reflective layer, as seen along the prism axis direction.

7. A light guide according to claim 6, further comprising:

a parallel guide formed of a pair of reflectors adjoining the thick end of the tapered guide.

8. A display apparatus comprising:

a light guide comprising;

a prismatic film with parallel prisms on its face;

a low-index film on the prisms; and

a cover layer on the low-index film, this layer having a substantially flat surface; and

a reflective layer facing the prismatic film; and

a light source arranged to inject light into the guide along the prism axis direction.

9. The display apparatus of claim 8 further comprising:

a display.