Brightness enhancement film with improved view angle

• US 20040109663A1
• Filed: 12/06/2002
• Published: 06/10/2004
• Est. Priority Date: 12/06/2002
• Status: Active Grant

• Current Assignee: Sabic Innovative Plastics IP BV (Government of Saudi Arabia)
• Original Assignee: General Electric Company
• Inventors: Olczak, Eugene
• Granted Patent: US 7,125,131 B2
• Time in Patent Office: Days
• US Class Current: 385/146
• CPC Class Codes: G02B 6/0001 specially adapted for lighting devices or systems lighting or signalling on vehicles using light guides B60Q1/00; lighting devices for vehicle dashboards B60Q3/10; lighting devices for vehicle interior using light guides B60Q3/62; lighting devices mounted on the vehicle rear part using light guides F21S43/235; measuring arrangements having light conducting pointers G01D13/265; illumination of liquid crystal displays G02F1/1336; illuminated signs G09F13/00
• CPC Class Codes: G02B 6/0031 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0038 Linear indentations or grooves, e.g. arc-shaped grooves or meandering grooves, extending over the full length or width of the light guide
• CPC Class Codes: G02B 6/0046 Tapered light guide, e.g. wedge-shaped light guide
• CPC Class Codes: G02B 6/005 provided by one optical element, or plurality thereof, placed on the light output side of the light guide
• CPC Class Codes: G02B 6/0071 with elongated shape, e.g. tube

Abstract

A structural shape on the surface of an optical substrate is such that the brightness of diffuse light departing from the surface of the optical substrate at certain off axis angles is reduced, at the expense of a small reduction in peak brightness measured near the viewing axis. The net result is an overall increase in useful illumination. A cross section of a prism as the structural shape has a curved sidewall or facet. A material with a relatively high index of refraction combined with a prismatic structure having a modified prism geometry improves brightness.

Claims

1. An optical substrate comprising:

a surface comprising a prism structure characterized by a cross section having a curved facet described by the equation

$z=\frac{{\mathrm{cr}}^2}{1+\sqrt{1-\left(1+k\right)<br><br>c^2<br><br>r^2}}+{\mathrm{dr}}^2+{\mathrm{er}}^4+{\mathrm{fr}}^6,$

wherein z is the perpendicular deviation of the surface of the facet of the prism from a straight line originating at a first reference point at a base of the prism and terminating at a second reference point near the peak of the prism and the coefficients of the polynomial lie within the following approximate ranges;

−

20<

c<

20;

−

10<

d<

10;

−

10<

e<

10;

−

10<

f<

10 and −

1<

k is less than or equal to zero and where r is a radial coordinate or distance from an optical axis.

2. The optical substrate as set forth in claim 1 wherein the prism structure comprises a plurality of prisms having a prescribed peak angle, α

, a height, h, a length, I, and a pitch, p.

3. The optical substrate as set forth in claim 2 wherein the plurality of prisms include at least a pseudorandom peak angle, α

, height, h, length, I, and pitch, p.

4. The optical substrate as set forth in claim 1 wherein a peak angle of the prism is greater than 90 degrees and the refractive index of the substrate is between approximately 1.65 and 1.8.

5. The optical substrate as set forth in claim 4 wherein the peak angle is 100 degrees.

18. The optical substrate as set forth in claim 1 wherein the prism structure is an ultraviolet curable organic or inorganic material.

22. The optical substrate as set forth in claim 1 wherein the prism structure includes a peak angle of greater than approximately 94 degrees and wherein c, d, e, f, and k are approximately equal to zero.

23. The optical substrate as set forth in claim 1 wherein the equation for z includes higher order terms in r defined by the summation

6. An optical substrate comprising:

a surface comprising a prism structure characterized by a peak angle of greater than 90 degrees and a refractive index of between approximately 1.65 and 1.8.

7. The optical substrate as set forth in claim 6 wherein the peak angle is 100 degrees.

19. The optical substrate as set forth in claim 6 wherein the prism structure is an ultraviolet curable organic or inorganic material.

8. A backlight display device comprising:

an optical source for generating light;

a light guide for guiding the light therealong including a reflective device positioned along the light guide for reflecting the light out of the light guide;

an optical substrate receptive of the light from the reflective device, the optical substrate comprising;

a surface comprising a prism structure characterized by a cross section having a curved facet.

9. The backlight display device as set forth in claim 8 wherein the curved facet is described by a segment of a polynomial function.

10. The backlight display device as set forth in claim 8 wherein the segment of the polynomial function is described by the equation

11. The backlight display device as set forth in claim 8 wherein a peak angle of the prism is greater than 90 degrees and the refractive index of the substrate is between approximately 1.65 and 1.8.

12. The backlight display device as set forth in claim 11 wherein the peak angle is 100 degrees.

13. The backlight display device as set forth in claim 8 wherein the optical substrate is formed with an optically transparent material with an index of refraction between approximately 1.65 and 1.8.

14. The backlight display device as set forth in claim 10 wherein the optical substrate is formed with an optically transparent material with an index of refraction of approximately 1.75.

20. The backlight display device as set forth in claim 8 wherein the prism structure is an ultraviolet curable organic or inorganic material.

24. The optical substrate as set forth in claim 10 wherein the prism structure includes a peak angle of greater than approximately 94 degrees and wherein c, d, e, f, and k are approximately equal to zero.

25. The optical substrate as set forth in claim 10 wherein the equation for z includes higher order terms in r defined by the summation

15. An optical substrate comprising:

a surface comprising a prism structure characterized by a cross section having a plurality of facets including a first facet oriented at a first angle with respect to the surface of the prism and a second facet oriented at a second angle with respect to the surface of the prism;

wherein the first and second facets intersect at one side of a centerline of the prism and the first and second angles are different.

16. The optical substrate as set forth in claim 15 wherein a peak angle of the prism structure is greater than 90 degrees and the refractive index of the substrate is between approximately 1.65 and 1.8.

17. The optical substrate as set forth in claim 16 wherein the peak angle is 100 degrees.

21. The optical substrate as set forth in claim 15 wherein the prism structure is an ultraviolet curable organic or inorganic material.

26. An optical substrate comprising:

a surface comprising a prism structure characterized by a cross section having a facet described by the equation

$z=\frac{{\mathrm{cr}}^2}{1+\sqrt{1-\left(1+k\right)<br><br>c^2<br><br>r^2}},$

wherein z is the perpendicular deviation of the surface of the facet of the prism from a straight line originating at a first reference point at a base of the prism and terminating at a second reference point near the peak of the prism.

27. The optical substrate as set forth in claim 26 wherein the equation further comprises thea summation of higher order terms

+dr²+er⁴+fr⁶

wherein the coefficients thereof lie within the following approximate ranges:

−

20<

c<

20;

−

10<

d<

10;

−

10<

e<

10;

−

10<

f<

10 and −

1<

k is less than or equal to zero and where r is a radial coordinate or distance from an optical axis.

28. An optical substrate comprising:

a surface comprising a prism structure characterized by a cross section having a plurality of facets intersecting at a peak so as to subtend a peak angle of α

.

29. The optical substrate as set forth in claim 28 wherein the plurality of facets form one or more compound facets respectively subtending an angle of β

or θ

with a base of the prism.