Backlight and display system using same

• US 8,469,575 B2
• Filed: 05/19/2008
• Issued: 06/25/2013
• Est. Priority Date: 05/20/2007
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Weber, Michael F., Hebrink, Timothy J., Nevitt, Timothy J., Wheatley, John A., Schardt, Craig R., Biernath, Rolf W., Bryan, William J., Ouderkirk, Andrew J., Freier, David G., Jordan, Myron K., Derks, Kristopher J., Yang, Zhaohui, Kivel, Edward J.
• Primary Examiner(s): CARTER, WILLIAM JOSEPH
• Application Number:
  US12/600,914
• Publication Number:
  US 20100165660A1
• Time in Patent Office: 1,863 Days
• Field of Search: 362600-634
• US Class Current: 362/609
• CPC Class Codes: F21V 7/04 Optical design
• CPC Class Codes: G02B 27/286 for controlling or changing the state of polarisation, e.g. transforming one polarisation state into another G02B5/3083 takes precedence; light guide coupling means utilising polarising elements G02B6/34
• CPC Class Codes: G02B 5/305 including organic materials, e.g. polymeric layers
• CPC Class Codes: G02B 5/3083 Birefringent or phase retarding elements G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001
• CPC Class Codes: G02B 6/0096 the lights guides being of the hollow type
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one

Abstract

A backlight that includes a front reflector and a back reflector that form a hollow light recycling cavity including an output surface is disclosed. The backlight further includes one or more light sources disposed to emit light into the light recycling cavity. The front reflector includes an on-axis average reflectivity of at least 90% for visible light polarized in a first plane, and an on-axis average reflectivity of at least 25% but less than 90% for visible light polarized in a second plane perpendicular to the first plane.

Claims

1. A backlight, comprising:

a front reflector and a back reflector that form a hollow light recycling cavity comprising an output surface; and

one or more light sources disposed to emit light into the light recycling cavity;

wherein the front reflector comprises a first asymmetric reflective film comprising alternating polymer layers, and further wherein the front reflector comprises an on-axis average reflectivity of at least 90% for visible light polarized in a first plane, and an on-axis average reflectivity of at least 25% but less than 90% for visible light polarized in a second plane perpendicular to the first plane.

2. The backlight of claim 1, wherein the one or more light sources comprise one or LEDs.

3. The backlight of claim 1, wherein the back reflector comprises an on-axis average reflectivity of at least 95% for visible light of any polarization.

4. The backlight of claim 1, wherein the front reflector comprises a first on-axis average transmissivity for visible light polarized in the first plane, and a second on-axis average trausmissivity for visible light polarized in the second plane, and further wherein a ratio of the second on-axis transmissivity to the first on-axis transmissivity is at least 10.

5. The backlight of claim 4, wherein the ratio is at least 20.

6. The backlight of claim 1, wherein p-polarized visible light that is polarized in the second plane exhibits a substantially constant average reflectivity as angle of incidence with the front reflector increases from near zero degrees to 60 degrees.

9. The backlight of claim 1, wherein the front reflector further comprises a second asymmetric, reflective film comprising alternating polymer layers positioned proximate the first asymmetric reflective film.

10. The backlight of claim 9, wherein the first asymmetric reflective film is attached to the second asymmetric reflective film using an optical adhesive.

11. The backlight of claim 1, wherein at least one of the front and back reflectors reflects light semi-specularly.

12. The backlight of claim 1, further comprising, side reflectors disposed about the periphery of the hollow light recycling cavity to substantially enclose the recycling cavity, the side reflectors having an on-axis average reflectivity of at least 95% for visible light of any polarization.

7. The backlight of claim wherein p-polarized visible light that is polarized in the second plane exhibits an increasing average reflectivity as angle of incidence with the front reflector increases from near zero degrees to 60 degrees.

8. The backlight of claim 7, wherein the increasing average reflectivity of the p-polarized light is substantially similar to an increasing average reflectivity of s-polarized visible light that is polarized in the second plane as angle of incidence with the front reflector increases from near zero degrees to 60 degrees.

13. A display system, comprising:

a display panel; and

a backlight disposed to provide light to the display panel, the backlight comprising;

a front reflector and a back reflector that form a hollow light recycling cavity comprising an output surface; and

one or more light sources disposed to emit light into the light recycling cavity;

wherein the front reflector comprises a first asymmetric reflective film comprising alternating polymer layers, and further wherein the from reflector comprises an on-axis average reflectivity of at least 90% for visible light polarized in a first plane, and an on-axis average reflectivity of at least 25% but less than 90% for visible light polarized in a second plane perpendicular to the first plane.