Brewster angle film for light management in luminaires and other lighting systems

• US 8,662,687 B2
• Filed: 11/17/2009
• Issued: 03/04/2014
• Est. Priority Date: 11/19/2008
• 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.
• Primary Examiner(s): MAI, ANH T
• Assistant Examiner(s): Santonocito, Michael
• Application Number:
  US13/129,430
• Publication Number:
  US 20110228511A1
• Time in Patent Office: 1,568 Days
• Field of Search: 362/19, 359/485.03, 359/586
• US Class Current: 362/19
• CPC Class Codes: G02B 5/305 including organic materials, e.g. polymeric layers
• 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: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/133543 Cholesteric polarisers
• CPC Class Codes: G02F 1/133545 Dielectric stack polarisers
• CPC Class Codes: G02F 1/1336 Illuminating devices
• CPC Class Codes: G02F 1/133606 including a specially adapted diffusing, scattering or light controlling members
• CPC Class Codes: G02F 1/133607 the light controlling member including light directing or refracting elements, e.g. prisms or lenses
• 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 1/133634 the refractive index Nz perpendicular to the element surface being different from in-plane refractive indices Nx and Ny, e.g. biaxial or with normal optical axis
• CPC Class Codes: G02F 2413/12 Biaxial compensators

Abstract

Multilayer optical films are disclosed that exhibit high reflectivity at normal incidence for all polarizations but preferentially transmit high angle rays in one or two orthogonal planes of incidence. Both symmetrical and asymmetrical constructions are disclosed. The films can be used in direct-lit backlights and in lighting systems other than direct-lit backlights, such as edge-lit backlights, and non-backlight lighting systems such as systems intended for general illumination without the need for any graphic component, such as luminaires and task lights.

Claims

1. A lighting system, comprising:

a light source; and

a multilayer optical film disposed to reflect some light from the light source and to transmit other light from the light source, the multilayer optical film having a first internal Brewster angle associated with a first in-plane axis and a second internal Brewster angle associated with a second in-plane axis orthogonal to the first in-plane axis, the second internal Brewster angle being different from the first internal Brewster angle.

2. The system of claim 1, wherein the system comprises a luminaire.

3. The system of claim 2, wherein the luminaire comprises a stiff light-transmissive panel.

4. The system of claim 3, wherein the multilayer optical film attaches to the panel.

5. The system of claim 4, wherein the multilayer optical film is laminated to the panel with substantially no intervening air gap.

6. The system of claim 1, wherein the system comprises a backlight.

7. The system of claim 6, wherein the backlight is an edge-lit backlight.

8. The system of claim 1, wherein the first in-plane axis is a strong axis and the second in-plane axis is a weak axis, and wherein the multilayer optical film reflects at least 75% of normally incident light in an extended wavelength band polarized parallel to the strong axis, and the multilayer optical film reflects at least 50% of normally incident light in the extended wavelength band polarized parallel to the weak axis.

9. The system of claim 8, wherein the multilayer optical film exhibits a first decrease in reflectivity as a function of incidence angle for p-polarized light incident in a first plane containing the strong axis, and the film exhibits a second decrease in reflectivity as a function of incidence angle for p-polarized light incident in a second plane containing the weak axis, and wherein the second decrease in reflectivity is stronger than the first decrease in reflectivity.

10. The system of claim 9, wherein the second decrease in reflectivity decreases by at least 50% at a particular oblique angle θ

oblique relative to normal incidence.

11. The system of claim 9, wherein the first decrease in reflectivity decreases by at least 40% at a particular oblique angle θ

oblique relative to normal incidence.

12. The system of claim 1, further comprising a structured surface layer coupled to the multilayer optical film.

13. The system of claim 12, wherein the structured surface layer comprises a prismatic film.

14. The system of claim 12, wherein the structured surface layer converts a wide angle batwing transmission characteristic of the multilayer optical film to a narrower angle batwing transmission characteristic.

15. The system of claim 12, wherein the structured surface comprises a 2-dimensional structure.

16. A lighting system, comprising:

a light source; and

a multilayer optical film disposed to reflect some light from the light source and to transmit other light from the light source, the multilayer optical film having an internal Brewster angle associated with each of two orthogonal in-plane axes, at least one of the internal Brewster angles corresponding to an incidence angle in air of less than 90 degrees.

17. The system of claim 16, further comprising a back reflector disposed to form a light recycling cavity with the multilayer optical film, the back reflector having a transport ratio T<

0.

18. The system of claim 16, further comprising a back reflector disposed to form a light recycling cavity with the multilayer optical film, the recycling cavity having a cavity transport CT<

0.25.