Backlighting system with faceted light pipes

• US 5,202,950 A
• Filed: 09/23/1991
• Issued: 04/13/1993
• Est. Priority Date: 09/27/1990
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Compaq Computer Corporation (HP Inc.)
• Inventors: Hathaway, Kevin J., Kornfuehrer, Gaylon R., Arego, Douglas A., Knox, Richard M. Jr.
• Primary Examiner(s): Epps, Georgia Y.
• Application Number:
  US07/764,427
• Time in Patent Office: 568 Days
• Field of Search: 359/50, 359/48, 385/146, 385/33, 385/901, 385/129, 362/27, 362/31, 362/32, 362/309, 362/341, 362/260, 362/227
• US Class Current: 385/146
• CPC Class Codes: F21V 7/00 Reflectors for light sources characterised by cooling arrangements F21V29/505
• CPC Class Codes: G02B 6/0001 specially adapted for lighting devices or systems lighting or signalling on vehicles using light guides B60Q1/00; lighting devices for vehicle dashboards B60Q3/10; lighting devices for vehicle interior using light guides B60Q3/62; lighting devices mounted on the vehicle rear part using light guides F21S43/235; measuring arrangements having light conducting pointers G01D13/265; illumination of liquid crystal displays G02F1/1336; illuminated signs G09F13/00
• CPC Class Codes: G02B 6/0046 Tapered light guide, e.g. wedge-shaped light guide
• CPC Class Codes: G02B 6/0048 with stepwise taper
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side
• CPC Class Codes: Y10S 385/901 Illuminating or display apparatus

Abstract

A light pipe used for backlighting liquid crystal displays has a planar front surface and a stair-stepped or faceted back surface. Light is injected from the ends of the light pipe from cold- or hot-cathode, apertured, fluorescent lamps. The cold-cathode lamps are preferably insulated to raise their operating temperature. The back surface has a series of planar portions parallel to the front surface connected by facets, which are angled so that the injected light reflects off the facets and through the front surface. A reflector having a planar, highly reflective, highly scattering surface or a sawtoothed or grooved upper surface in located adjacent to and parallel with the light pipe back surface to reflect light escaping from the back surface back through the light pipe to exit the front surface. The axis of grooves is preferably slightly skewed from the facet axis to reduce moire pattern development. A low-scattering or low-loss diffuser is located adjacent to and parallel with the light pipe front surface to reduce moire pattern development. The liquid crystal display is located over the low scattering diffuser. A separate injector may be located between the lamp and the light pipe to better couple the light into the light pipe. Light pipes may be stacked to provide a backlight system having increased brightness and/or greater viewing angle.

Claims

1. A backlighting system for a liquid crystal display, said system having an illuminated front surface, comprising:

a first faceted light pipe proximal the illuminated front surface of the backlight having a generally planar front surface for providing light to said illuminated front surface, having a faceted back surface wherein said back surface includes a plurality of generally planar portions parallel to said front surface and a plurality of facets formed at an angle to said front surface and located connecting said back surface parallel portions, and having at least one end surface for receiving light to be transmitted through said front surface;

a first light source means located adjacent said end surface for receiving light of said first faceted light pipe for providing light to said first light pipe;

a second faceted light pipe proximal the back surface of the first faceted light pipe having a generally planar front surface situated such that light exiting said front surface enters the back surface of the first faceted light pipe, having a faceted back surface wherein said back surface includes a plurality of generally planar portions parallel to said front surface and a plurality of facets formed at an angle to said front surface and located connecting said back surface parallel portions, and having at least one end surface for receiving light to be transmitted through said front surface; and

,

a second light source means located adjacent said end surface for receiving light of said second faceted light pipe for providing light to said second light pipe.

2. A backlighting system as recited in claim 1 wherein the first light source means and the second light source means are situated on the same side of the backlight.

3. A backlighting system as recited in claim 1 wherein the first light source means and the second light source means are situated on opposing sides of the backlight.

4. A backlighting system for a liquid crystal display, said system having an illuminated front surface, comprising:

a first faceted light pipe proximal the illuminated front surface of the backlight having a generally planar front surface for providing light to said illuminated front surface, having a faceted back surface wherein said back surface includes a plurality of generally planar portions parallel to said front surface and a plurality of facets formed at an angle to said front surface and located connecting said back surface parallel portions, and having at least one end surface for receiving light to be transmitted through said front surface;

a first light source means located adjacent said end surface for receiving light of said first faceted light pipe for providing light to said first light pipe;

a second faceted light pipe proximal the back surface of the first faceted light pipe having a generally planar front surface situated such that light exiting said front surface enters the back surface of the first faceted light pipe, having a faceted back surface wherein said back surface includes a plurality of generally planar portions parallel to said front surface and a plurality of facets formed at an angle to said front surface and located connecting said back surface parallel portions, and having at least one end surface for receiving light to be transmitted through said front surface;

light source means located adjacent the faceted back surface of the second faceted light pipe; and

,

light transmission means for directing the light from the light source means to the end surfaces for receiving light of the first and second faceted light pipes.

5. A backlighting system as recited in claim 4 wherein the light transmission means is a light pipe.

6. The backlighting system of claim 4 further comprising at least one lens situated between the light source means and the light transmission means.

7. A backlighting system as recited in claim 6 wherein the light source means is an apertured fluorescent lamp having a plurality of discrete apertures and at least one lens is aligned so as to receive and focus light exiting from at least one aperture of the lamp.