Recycling backlights with semi-specular components

• US 9,091,408 B2
• Filed: 11/18/2013
• Issued: 07/28/2015
• 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., Nevitt, Timothy J., Wheatley, John A., Biernath, Rolf W., Freier, David G., Benoit, Gilles J., Hoyle, Charles D., Ouderkirk, Andrew J., Yang, Zhaohui
• Primary Examiner(s): HAN, JASON
• Application Number:
  US14/082,788
• Publication Number:
  US 20140071658A1
• Time in Patent Office: 617 Days
• Field of Search: 362 971- 974, 362/249.02, 362/296.01, 362297-298, 362/301, 362/341, 362/346, 362/800, 349 61- 62, 349/67
• US Class Current: 1/1
• CPC Class Codes: F21K 9/60 Optical arrangements integrated in the light source, e.g. for improving the colour rendering index or the light extraction
• CPC Class Codes: F21V 7/00 Reflectors for light sources characterised by cooling arrangements F21V29/505
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0056 for producing polarisation effects, e.g. by a surface with polarizing properties or by an additional polarizing elements
• CPC Class Codes: G02B 6/0096 the lights guides being of the hollow type
• CPC Class Codes: G02F 1/133605 including specially adapted reflectors
• CPC Class Codes: G02F 1/133606 including a specially adapted diffusing, scattering or light controlling members
• CPC Class Codes: G02F 1/133611 including means for improving the brightness uniformity
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one

Abstract

A recycling cavity such as used in a backlight or similar extended area source includes a front and back reflector, the front reflector being partially transmissive to provide an output illumination area. The recycling cavity also includes a component that provides the cavity with a balance of specular and diffuse characteristics so as to balance cavity efficiency and brightness uniformity over the output area. The component can be characterized by a transport ratio of greater than 15% for a 15 degree incidence angle, and less than 95% for a 45 degree incidence angle.

Claims

1. A backlight, comprising:

a front and back reflector forming a hollow light recycling cavity, the front reflector being partially transmissive to provide an output illumination area, and wherein the front reflector has a reflectivity for p-polarized light that is;

(1) constant, or (2) increases, with angle of incidence, and a transmission that generally decreases with angle of incidence;

a component that provides the cavity with a desired balance of specular and diffuse characteristics, the component being characterized by a transport ratio greater than 15% at a 15 degree incidence angle and less than 95% at a 45 degree incidence angle, wherein the front or back reflectors can be or include the component, or the component can be distinct from the front and back reflectors, wherein the transport ratio for the component, for light of a given incidence angle, equals (F−

B)/(F+B), where F is the amount of light scattered into forward directions upon interaction of the incident light with the component, and B is the amount of light scattered into backward directions upon interaction of the incident light with the component; and

one or more light source members disposed to emit light into the light recycling cavity over a limited angular distribution.

2. The backlight of claim 1, wherein the front reflector has a hemispherical reflectivity for unpolarized visible light of R^f_hemi, the back reflector has a hemispherical reflectivity for unpolarized visible light of R^b_hemi, and R^b_hemi is greater than R^f_hemi.

3. The backlight of claim 2, wherein R^b_hemi is greater than about 0.95.

4. The backlight of claim 1, wherein the output illumination area defines a transverse plane, and the light source members emit light into the light recycling cavity with a full angle-width at half maximum power (FWHM) relative to the transverse plane in a range from 0 to 60 degrees.

5. The backlight of claim 4, wherein the light source members emit light into the light recycling cavity with an FWHM relative to the transverse plane in a range from 0 to 30 degrees.

6. The backlight of claim 1, wherein the light source members include one or more LEDs.

7. The backlight of claim 1, wherein the reflectivity and transmission of the front reflector are for unpolarized visible light in any plane of incidence.

8. The backlight of claim 1, wherein the reflectivity and transmission of the front reflector are for light of a useable polarization state incident in a plane for which oblique light of the useable polarization state is p-polarized.

9. A luminaire comprising the backlight of claim 1.

10. A display comprising the backlight of claim 1.

11. A backlight, comprising:

a front and back reflector forming a light recycling cavity, the front reflector being partially transmissive to provide an output illumination area, and wherein the front reflector has a reflectivity for p-polarized light that is;

(1) constant, or (2) increases, with angle of incidence, and a transmission that generally decreases with angle of incidence;

a component that provides the cavity with a desired balance of specular and diffuse characteristics, the component being characterized by a transport ratio greater than 15% at a 15 degree incidence angle and less than 95% at a 45 degree incidence angle, wherein the front or back reflectors can be or include the component, or the component can be distinct from the front and back reflectors, wherein the transport ratio for the component, for light of a given incidence angle, equals (F−

B)/(F+B), where F is the amount of light scattered into forward directions upon interaction of the incident light with the component, and B is the amount of light scattered into backward directions upon interaction of the incident light with the component; and

one or more light source members disposed to emit light into the light recycling cavity over a limited angular distribution;

wherein the cavity comprises a cavity transport value of greater than about 0.5 and less than about 0.95.

12. The backlight of claim 11, wherein the front reflector has a hemispherical reflectivity for unpolarized visible light of R^f_hemi, the back reflector has a hemispherical reflectivity for unpolarized visible light of R^b_hemi, R_bhemi is greater than R^f_hemi, and R^b_hemi is greater than about 0.95.

13. The backlight of claim 11, wherein the output illumination area defines a transverse plane, and the light source members emit light into the light recycling cavity with a full angle-width at half maximum power (FWHM) relative to the transverse plane in a range from 0 to 60 degrees.

14. The backlight of claim 13, wherein the light source members emit light into the light recycling cavity with an FWHM relative to the transverse plane in a range from 0 to 30 degrees.

15. The backlight of claim 11, wherein the reflectivity and transmission of the front reflector are for unpolarized visible light in any plane of incidence.

16. The backlight of claim 11, wherein the reflectivity and transmission of the front reflector are for light of a useable polarization state incident in a plane for which oblique light of the useable polarization state is p-polarized.

17. The backlight of claim 11, wherein the light recycling cavity is hollow.

18. A luminaire comprising the backlight of claim 11.

19. A display comprising the backlight of claim 11.