Brightness enhancement film for backlit image displays

• US 7,286,280 B2
• Filed: 03/16/2005
• Issued: 10/23/2007
• Est. Priority Date: 05/07/2004
• Status: Expired due to Fees

• Current Assignee: University of British Columbia
• Original Assignee: University of British Columbia
• Inventors: Whitehead, Lorne A., Mossman, Michele Ann
• Primary Examiner(s): Mack; Ricky
• Assistant Examiner(s): TRA, TUYEN Q
• Application Number:
  US11/080,565
• Publication Number:
  US 20050248848A1
• Time in Patent Office: 951 Days
• Field of Search: 359/296, 359/263, 359/222, 359/620, 359/253, 359/252, 345/84, 348/759, 349/62
• US Class Current: 359/296
• CPC Class Codes: G02B 3/0031 Replication or moulding, e.g. hot embossing, UV-casting, injection moulding
• CPC Class Codes: G02B 3/0043 Inhomogeneous or irregular arrays, e.g. varying shape, size, height
• CPC Class Codes: G02B 3/005 arranged along a single direction only, e.g. lenticular sheets G02B3/0043 takes precedence
• CPC Class Codes: G02B 3/0062 Stacked lens arrays, i.e. refractive surfaces arranged in at least two planes, without structurally separate optical elements in-between
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• CPC Class Codes: G02F 1/133606 including a specially adapted diffusing, scattering or light controlling members

Abstract

A brightness enhancement film having a monolayer of approximately hemispherical, transparent, closely packed larger diameter hemi-beads. Due to the hemi-beads'"'"' hemispherical shape, gaps remain between adjacent ones of the larger diameter hemi-beads. A substantial number of the gaps are provided with at least one approximately hemispherical, transparent hemi-bead having a diameter substantially less than the diameter of the larger diameter hemi-beads. Provision of smaller diameter hemi-beads within the gaps increases the film'"'"'s reflectance value, such that the film'"'"'s apparent brightness declines as a relatively smooth, continuous function of viewing angle, for viewing angles ranging from 0° (normal incidence) to about 40°, which is the preferred angular viewing range.

Claims

1. A backlit display having a brightness enhancement film mounted on an outward side of a light source of the display, the film comprising:

(a) a transparent sheet formed of a solid transparent dielectric material; and

(b) a first plurality of hemispherical solid transparent dielectric hemi-beads substantially covering and protruding outwardly from an outward surface of the sheet on an outward side of the light source.

2. A backlit display as defined in claim 1, wherein at least some of the hemi-beads have a minimum diameter of 2 microns.

3. A backlit display as defined in claim 1, wherein the sheet has a refractive index of at least 1.5 and the hemi-beads have a refractive index of at least 1.5.

4. A backlit display as defined in claim 1, wherein the sheet has a refractive index of at least 1.6 and the hemi-beads have a refractive index of at least 1.6.

5. A backlit display as defined in claim 1, wherein the first plurality of hemi-beads are closely packed in a monolayer.

6. A backlit display as defined in claim 1, wherein the first plurality of hemi-beads are hemispherical portions of spherical members partially embedded in the sheet.

7. A backlit display as defined in claim 1, wherein the first plurality of hemi-beads are hemispherical members affixed to the outward surface of the sheet.

8. A backlit display as defined in claim 1, further comprising a microreplicated prism film substantially macroscopically parallel to and on an inward side of the brightness enhancement film.

9. A backlit display as defined in claim 1, wherein the brightness enhancement film is a first brightness enhancement film, the display further comprising a second brightness enhancement film substantially macroscopically parallel to the first brightness enhancement film, the second brightness enhancement film further comprising a second plurality of hemi-spherical solid transparent dielectric hemi-beads substantially covering and protruding outwardly from an outward surface of the second brightness enhancement film on an outward side of the light source.

15. A brightness enhancement film as defined in claim 3, wherein the first plurality of hemi-beads are hemispherical portions of spherical members partially embedded in the sheet and the second plurality of hemi-beads are approximately hemispherical portions of approximately spherical members partially embedded in the sheet.

10. A brightness enhancement film for mounting on an outward side of a light source of a backlit display, the film comprising:

(a) a transparent sheet formed of a solid transparent dielectric material;

(b) a first plurality of approximately hemispherical solid transparent dielectric hemi-beads substantially covering and protruding outwardly from an outward surface of the sheet, at least some of the hemi-beads having a minimum diameter of 2 microns;

(c) a gap between adjacent ones of the first plurality of hemi-beads; and

(d) at least some of the gaps containing at least one of a second plurality of approximately hemispherical solid transparent dielectric hemi-beads, each one of the second plurality of hemi-beads having a second average diameter less than the first average diameter.

11. A brightness enhancement film as defined in claim 10, wherein the sheet has a refractive index of at least 1.5 and the hemi-beads have a refractive index of at least 1.5.

12. A brightness enhancement film as defined in claim 10, wherein the sheet has a refractive index of at least 1.6 and the hemi-beads have a refractive index of at least 1.6.

13. A brightness enhancement film as defined in claim 10, wherein the first plurality of hemi-beads and the second plurality of hemi-beads are closely packed in a monolayer.

14. A brightness enhancement film as defined in claim 10, wherein at least 75% of the gaps containing at least one of the second plurality of hemi-beads.

16. A brightness enhancement film as defined in claim 10, wherein the first plurality of hemi-beads are hemispherical members affixed to the outward surface of the sheet and the second plurality of hemi-beads are approximately hemispherical members affixed to the outward surface of the sheet.

17. The backlit display having a brightness enhancement film as defined in claim 10.

18. The backlit display having substantially macroscopically parallel inward and outward brightness enhancement films, the inward film further comprising a microreplicated prism brightness enhancement film, and the outward film further comprising a brightness enhancement film as defined in claim 10.

19. The backlit display having substantially macroscopically parallel inward and outward brightness enhancement films, the inward film and the outward film each further comprising a brightness enhancement film as defined in claim 10.

20. A method of enhancing the brightness of a backlit display, the method comprising:

(a) providing an outward surface on an outward side of a light source of the display with a first sheet formed of a solid transparent dielectric material;

(b) substantially covering an outward surface of the first sheet with a first plurality of outwardly protruding, hemispherical solid transparent hemi-beads; and

(c) guiding light rays emitted by the display through the first sheet and hemi-beads.

21. A method as defined in claim 20, further comprising closely packing the first plurality of hemi-beads in a monolayer.

22. A method as defined in claim 20, further comprising providing a second sheet formed of a solid transparent dielectric material, aligning the second sheet substantially macroscopically parallel to and inwardly of the first sheet, providing a plurality of microreplicated prisms on the second sheet, and guiding the light rays through the second sheet toward the first sheet.

23. A method as defined in claim 22, further comprising providing the plurality of microreplicated prisms on an outward surface of the second sheet.

24. A method of enhancing the brightness of a backlit display, the method comprising:

(a) providing an outward surface on an outward side of a light source of the display with a first sheet formed of a solid transparent dielectric material;

(b) substantially covering an outward surface of the first sheet with a first plurality of outwardly protruding, hemispherical solid transparent hemi-beads; and

(c) guiding light rays emitted by the display through the first sheet and hemi-beads;

wherein a gap remains between adjacent ones of the first plurality of hemi-beads and wherein the first plurality of hemi-beads have a first average diameter, the method further comprising providing, in at least some of the gaps, at least one of a second plurality of approximately hemispherical transparent high refractive index hemi-beads, each one of the second plurality of hemi-beads having an second average diameter less than the first average diameter.

25. A method as defined in claim 24, further comprising closely packing the first plurality of hemi-beads and the second plurality of hemi-beads in a monolayer.

26. A method as defined in claim 24, further comprising providing at least one of the second plurality of hemi-beads in at least 75% of the gaps.

27. A method as defined in claim 24, further comprising providing a second sheet formed of a solid transparent dielectric material, aligning the second sheet substantially macroscopically parallel to and inwardly of the first sheet, substantially covering an outward surface of the second sheet with a second plurality of outwardly protruding, hemispherical solid transparent hemi-beads, and guiding the light rays through the second sheet toward the first sheet.