RECYCLING BACKLIGHTS WITH SEMI-SPECULAR COMPONENTS

• US 20100238686A1
• Filed: 05/19/2008
• Published: 09/23/2010
• 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: Wheatley, John A., Weber, Michael F., Biernath, Rolf W., Nevitt, Timothy J., Benoit, Gilles J., Hoyle, Charles D., Ouderkirk, Adrew J., Yang, Zhachui, Freier, David G.
• Granted Patent: US 8,608,363 B2
• Time in Patent Office: Days
• US Class Current: 362/609
• 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 hollow light-recycling backlight has a “semi-specular” component providing a balance of specularly and diffusely reflected light improving the uniformity of the light output. The component may be arranged on the reflectors (1021), (1014) or inside the cavity (1016). This balance is achieved by designing the component'"'"'s “transport ratio” defined by (F−B)/(F+B), (F and B are the amounts of incident light scattered forwards and backwards respectively by the component in the plane of the cavity) to lie in a certain range. Furthermore, the product of the front and back reflector “hemispherical” reflectivities should also lie in a given range. Alternatively, the “cavity transport value”, a measure of how well the cavity can spread injected light from the injection point to distant points in the cavity should lie in a further range and the “hemispherical” reflectivity of the back reflector should be >0.7.

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;

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; and

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

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 0.70.

2. The backlight of claim 1, wherein the transport ratio is greater than 20% at a 15 degree incidence angle.

3. The backlight of claim 1, wherein the transport ratio is less than 90% at a 45 degree incidence angle.

4. The backlight of claim 1, 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 backwards directions upon interaction of the incident light with the component.

5. 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.

6. The backlight of claim 5, 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.

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

8. The backlight of claim 1, wherein the front reflector has a reflectivity that generally increases with angle of incidence, and a transmission that generally decreases with angle of incidence.

9. The backlight of claim 8, where the reflectivity and transmission of the front reflector are for unpolarized visible light in any plane of incidence.

10. The backlight of claim 8, 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.

11. The backlight of claim 1, wherein R^f_hemi*R^b_hemi is at least 0.75.

12. The backlight of claim 11, wherein R^f_hemi*R^b_hemi is at least 0.80.

13. A hollow light recycling cavity comprising a front and back reflector, the front reflector being partially transmissive to provide an output illumination area, wherein the cavity comprises a cavity transport value of greater than about 0.5 and less than about 0.95, and further wherein the front reflector comprises an R_hemi of greater than about 0.7.

14. The cavity of claim 13, further comprising a component that provides the cavity with a desired balance of specular and diffuse characteristics, wherein the front or back reflectors can be or include the component, or the component can be distinct from the front and back reflectors.