Illumination systems with sloped transmission spectrum front reflector

• US 9,441,809 B2
• Filed: 10/17/2012
• Issued: 09/13/2016
• Est. Priority Date: 10/20/2011
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Nevitt, Timothy J., Weber, Michael F., Wheatley, John A., Sousa, Matthew E., Liu, Tao
• Primary Examiner(s): TSO, LAURA K
• Application Number:
  US14/352,860
• Publication Number:
  US 20140254125A1
• Time in Patent Office: 1,427 Days
• Field of Search: 362/97.1, 362/97.2, 362/97.3, 362/600
• US Class Current: 1/1
• CPC Class Codes: F21V 13/08 the elements being filters or photoluminescent elements and reflectors
• CPC Class Codes: F21V 7/04 Optical design
• CPC Class Codes: G02B 5/305 including organic materials, e.g. polymeric layers
• CPC Class Codes: G02B 6/0031 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0063 for extracting light out both the major surfaces of the light guide
• CPC Class Codes: G02B 6/0096 the lights guides being of the hollow type
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: G02F 1/133605 including specially adapted reflectors
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side

Abstract

A backlight (10) includes a front and back reflectors (12,14) forming a light recycling cavity (16) and one or more light source members (24a, 24b, 24c) disposed to emit light into the light recycling cavity. The front reflector (12) being partially reflective to provide an output illumination area. The front reflector (12) has a blue sloped transmission spectra, at normal incidence with a range among bin values from 15% to 100%.

Claims

1. A backlight comprising:

a front and back reflector forming a light recycling cavity, the front reflector being partially reflective to provide an output illumination area; and

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

wherein the front reflector has a hemispherical reflectivity for unpolarized visible light of R^f_hemi, and the back reflector has a hemispherical reflectivity for unpolarized visible light of R^b_hemi, and R^f_hemi*R^b_hemi is at least 0.65;

and wherein the front reflector has a sloped transmission spectra at a view angle of interest Ω

, and a backlight intensity spectrum;

T(Ω

,λ

)/{1−

R^b_hemi(λ

)*R^f_Hemi(λ

)}

is substantially neutral across a visible wavelength band.

2. A backlight according to claim 1, wherein R^f_hemi*R^b_hemi is at least 0.75.

3. A backlight according to claim 1, wherein R^f_hemi*R^b_hemi is at least 0.85.

4. A backlight according to claim 1, wherein the front reflector comprises a polarizer.

5. A backlight according to claim 1, wherein the front reflector comprises a reflective polarizer.

6. A backlight according to claim 1, wherein the backlight illuminates a liquid crystal display panel.

7. A backlight according to claim 5, wherein the front reflector comprises an absorbing polarizer.

8. A backlight comprising:

a front and back reflector forming a light recycling cavity, the front reflector being partially reflective to provide an output illumination area;

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

wherein the front reflector has a hemispherical reflectivity for unpolarized visible light of R^f_hemi, and the back reflector has a hemispherical reflectivity for unpolarized visible light of R^b_hemi, and R^f_hemi*R^b_hemi is at least 0.65;

and wherein the front reflector has a sloped transmission spectra at a view angle of interest χ

, and a backlight intensity spectrum

T(Ω

,λ

)/{1−

R^b_hemi(λ

)*R^f_Hemi(λ

)}

is substantially blue-sloped across a visible wavelength band.

9. A backlight according to claim 8, wherein R^f_hemi*R^b_hemi is at least 0.75.

10. A backlight according to claim 8, wherein R^f_hemi*R^b_hemi is at least 0.85.

11. A backlight according to claim 8, wherein the front reflector comprises a polarizer.

12. A backlight according to claim 8, wherein the front reflector comprises a reflective polarizer.

13. A backlight according to claim 8, the backlight illuminates a liquid crystal display panel.

14. A backlight according to claim 12, wherein the front reflector comprises an absorbing polarizer.

15. A backlight comprising:

a front and back reflector forming a light recycling cavity, the front reflector being partially reflective to provide an output illumination area;

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

wherein the front reflector has a hemispherical reflectivity for unpolarized visible light of R^f_hemi, and the back reflector has a hemispherical reflectivity for unpolarized visible light of R^b_hemi, and R^f_hemi*R^b_hemi is at least 0.65;

and wherein the front reflector has a sloped transmission spectra at a view angle of interest Ω

, and a backlight intensity spectrum

T(,Ω

λ

)/{1−

R^b_hemi(λ

)*R^f_hemi(λ

)}

is substantially red-sloped across a visible wavelength band.

16. A backlight according to claim 15, wherein R^f_hemi*R^b_hemi is at least 0.85.

17. A backlight according to claim 15, wherein the front reflector comprises a polarizer.

18. A backlight according to claim 15, wherein the front reflector comprises a reflective polarizer.

19. A backlight according to claim 15, the backlight illuminates a liquid crystal display panel.

20. A backlight according to claim 18, wherein the front reflector comprises an absorbing polarizer.