Back light assembly for use with back-to-back flat-panel displays

Abstract

The present invention features a system for uniformly distributing luminance and a high degree of collimation from a back light module for flat-panel, liquid crystal displays (LCDs) simultaneously. A constant and uniform luminance output of the back light module in two directions is obtained through appropriate selection of lamps, geometry and optical components. An appropriate balance of lamps, lamp spacing, diffusers and light collimating optics are chosen to produce a high brightness back light module with very high intensity output over two very large surfaces. Variations in intensity over the illuminated area are minimized using light recycling in conjunction with the reflective diffusers and collimating optics. Precision collimators eliminate light beyond a defined angle, as required in tiled or monolithic flat-panel LCDs with predetermined display specifications.

Description

The light exiting rearward is the same as that exiting forward; thus, the total light exiting from the back light assembly is:

$L=\frac{Nl}{360}\left\{{\varphi }_{\mathrm{forward}}{\varphi }_{\mathrm{back}}\right\}$
where [1] l is the total light output of one lamp. The results are plotted in FIG. 4.

Since the power consumed by each lamp 128 is constant, efficiency is related to light output and the number of lamps. The curve 170 is nearly linear until the number of lamps approaches one-half of the maximum that can be installed in the allotted space. It is desirable then to choose a light output design point near this inflection point. Thus, an optimum number of lamps 168 are shown in FIG. 4.

Referring now to FIG. 5, there is shown a schematic, cross-sectional view 180 of the inventive back light assembly with back-to-back displays. Many optical components typically used in both single and back-to-back configurations are shown.

Light collimating optics 132 consist of crossed BEFs 182 and 184 and a collimator 186. The diffusers and collimating optics 132 are sandwiched between glass plates 188 and 190. These plates 188 and 190 may be optically clear, with enough stiffness to support the film optics over the expanse needed. Flat-panel displays 122 are placed in front of the optics assemblies 192 and separated by a distance F, leaving air spaces 194. These air spaces 194 are vented to ambient air to allow for further cooling of the displays 122.

As was previously stated, the collimating optics use BEFs which accept light at high angles of incidence and send light at near normal angles of incidence back towards the back light assembly for recycling. It is desirable to have as much reflective area available as possible for the BEFs. However, more lamps produce more light output. The first pass design choice for lamp spacing S is increased slightly. It has been found that increasing lamp spacing such that the number of lamps is reduced by approximately 10% provides satisfactory results. The coupling of light into the BEFs 182 and 184 is also affected by the distance B that they are placed from the lamps 128.

The luminance output of the BEFs increases with proximity to the lamps, but luminance uniformity decreases with proximity to the lamps. For practical purposes, a reasonable space H 146 is required between the lamps 128 and the glass optics holder for air flow to cool the cavity 126 (FIG. 2a).

The preferred diffuser 130 is a high efficiency, low transmission diffuser which is chosen to have a near Lambertian distribution in order to couple a maximum amount of light into the BEFs 182 and 184 and to permit a maximum amount of recycling in the back light cavity 126. The diffuser 130 must efficiently reflect light, it must have high transmission efficiency, and it must produce a Lambertian distribution of light. Additionally, the lamps are not 100% absorbing. Consequently, fine tuning is necessary in the design parameters of lamp spacing, back plane space, and BEF spacing to the lamps.

The collimators 186, also described in detail in the aforementioned U.S. Pat. No. 5,903,328, consist of open hexagonal cells in a honey comb configuration, coated with a highly light-absorbing paint. The aspect ratio of cell width to cell depth determines the cut-off angle or collimation angle.

The use of a sharp cut-off collimator is preferred in a seamless, tiled, flat-panel display. Non-tiled, large monolithic or monolithic-like displays do not require cut-off angles as sharp as those for tiled displays. A more efficient collimator design which may be applied is disclosed in United States Provisional Patent Application Serial No. 60/177,447. Unfortunately, collimators, having a physical structure, create a shadow image which can be seen on the display. To prevent imaging of the collimator, the display is placed a predetermined distance F away so that cell images overlap, or are defocused, and therefore are not visible to the viewer.

FIG. 6 depicts the degree of collimation or angular distribution of light emitted from each of the optical components. The diffuser 130 emits a Lambertian distribution 200, as stated hereinabove. The BEFs 182, 184 focus light forward in a distribution 202 that has a theoretical forward gain of 2.2 for the type used herein. Actual achieved forward gain is about 1.9. The BEF distribution 202 has a significant amount of light energy remaining beyond the cut-off angle (˜301 in the preferred embodiment) that is undesirable for use with seamless, tiled, flat-panel displays.

The collimator 186 eliminates such unwanted light by cutting off light beyond the collimation angle, as shown by its emission distribution 204. The surface absorption of the collimator cell must be sufficient to prevent luminance of more than 1% of normal luminance beyond the collimation angle.

Brightness levels far exceeding existing industry capability have been achieved with the inventive design. Luminance values exceeding 100,000 nits (candelas/square meter) have been reached. Reasonable designs with exceptional efficiency have been prototyped with luminance output exceeding 50,000 nits, a uniformity of luminance of 10% at an efficiency better than any currently available commercial back light unit, even those achieving lower brightness levels.

Since other modifications such as in optical configurations can be made to fit particular operating specifications and requirements, it will be apparent to those skilled in the art that the invention is not considered limited to the examples chosen for purposes of disclosure, and covers all changes and modifications which do not constitute departures from the true spirit and scope of this invention.

Having thus described the invention, what is desired to be protected by Letters Patent is presented in the subsequently appended claims.

Claims

1. A high-output back light module for use with two back-to-back flat-panel displays, comprising:

a) a housing having an open front and an open back and defining a lamp cavity, said lamp cavity having substantially solid, optically-reflective side walls;

b) an array of lamps disposed within said lamp cavity; and

c) lamp control means operatively connected to at least one lamp of said array of lamps to provide power thereto and to optimize light output therefrom;

wherein said housing, said lamp cavity and said lamp array are disposed intermediate two back-to-back flat-panel displays at a predetermined distance from each of said two back-to-back flat-panel displays.

2. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 1, wherein said lamp cavity is substantially rectangular and oriented such that the longer side of said rectangle is disposed horizontally.

3. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 2, wherein said array of lamps is disposed horizontally within said lamp cavity.

4. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 2, wherein said lamp array comprises fluorescent lamps.

5. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 4, wherein said fluorescent lamps comprise hot cathode fluorescent lamps.

6. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 5, further comprising at least one from group: collimating means, diffuser means and brightness enhancing films (BEFs) disposed intermediate said housing, and at least one of said back-to-back flat-panel displays.

7. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 6, wherein said lamp array is defined by parameters comprising the number of lamps in said lamp array, the type of lamps, the lamp diameter and the inter-lamp spacing, and wherein at least one of said parameters is chosen to optimize light. output from said lamp array disposed in said lamp cavity.

8. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 7, wherein lamps of said array of lamps are spaced apart from one another at a predetermined, inter-lamp spacing; said array of lamps being disposed a predetermined, optimized distance from each of said back-to-back flat-panel displays, said distance being functionally related to at least one of the parameters: lamp diameter, lamp type, inter-lamp spacing, collimator means, BEFs and diffusers.

9. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 8, wherein said inter-lamp spacing between each lamp of said array of lamps is substantially equal.

10. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 6, wherein said collimating means comprises a collimator having an array of open cells having a regular, repeating cell geometry, said geometry defining a cell width, each of said cells having a thickness defining a cell depth.

11. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 10, wherein said cell width and said cell depth have an aspect ratio therebetween, defining a cut-off angle.

12. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 11, wherein said cell width and said cell depth define cell walls.

13. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 12, wherein said cell walls are coated with a light-absorbing coating.

14. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 12, wherein said light-absorbing coating comprises flat, black paint.

15. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 8, further comprising a high efficiency exit diffuser placed proximate at least one of said open front and open back of said housing.

16. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 15, wherein said high efficiency exit diffuser produces a substantially lambertian distribution and efficiently reflects light for recirculation.

17. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 16, wherein said high efficiency exit diffuser is disposed at a predetermined distance from said lamps whereby luminance gradients are reduced across said illuminated areas below a predetermined value.

18. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 17, further comprising brightness-enhancing means disposed proximate said high efficiency exit diffuser.

19. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 18, wherein said brightness-enhancing means comprises at least two brightness-enhancing films (BEFs) for collimating light, disposed intermediate said lamps and at least one of said back-to-back displays, said BEFs comprising parallel V-grooves having a predetermined wall angle relative to a first surface thereof, said BEFs being arranged substantially orthogonally to one another.

20. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 19, wherein said first surfaces of said BEFs face away from said array of lamps, said BEFs interacting with said high efficiency exit diffusers to enhance the forward gain of light collimated by said collimating means.

21. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 1, wherein said lamp control means comprises lamp temperature regulation means adapted to maintain the surface temperature of each of said lamps within a predetermined range of operating temperatures.

22. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 21, wherein said lamp temperature regulation means comprises at least one from the group:

heat sinks, dimming controls and fan speed controls.

23. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 22, wherein at least one of said dimming controls and fan speed controls comprises a temperature sensor proximate at least one of said array of lamps.

24. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 23, wherein said temperature sensor generates a variable output voltage representative of the temperature of said at least one of said array of lamps.

25. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 24, wherein said temperature sensor generates a variable output voltage representative of the temperature of at least one of said lamps, said variable output voltage controlling the speed of a cooling fan.

26. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 24, wherein said temperature sensor generates a variable output voltage representative of the temperature of at least one of said lamps, said variable output voltage controlling the output of a dimming ballast.

27. The high-output back light module for use with back-to-back flat-panel displays as recited in claim 24, wherein said temperature sensor comprises a thermistor.

28. The high-output back light module for use with back-to-back flat-panel display as recited in claim 1, wherein at least one of said flat-panel displays comprises one from the group: monolithic display, monolithic-like display, tiled display.

29. A back light module comprising:

a diffuser having an incidence side and an output side;

a brightness enhancing film having an incidence side and an output side, the incidence side of the brightness enhancing film being faced toward the output side of the diffuser; and

a second diffuser having an opposing side that is disposed at a predetermined distance from the incidence side of the diffuser;

wherein the second diffuser produces a substantially lambertian distribution; and

wherein the incidence side of the diffuser at least partially transmits light toward the brightness enhancing film and at least partially reflects light transmitted from the output side of the diffuser back toward the brightness enhancing film, the opposing side of the second diffuser at least partially reflects light toward the diffuser.

30. The back light module as recited in claim 29, wherein the output side of the brightness enhancing film at least partially reflects light transmitted by the diffuser back toward the diffuser.

31. The back light module as recited in claim 30, further comprising another brightness enhancing film, the brightness enhancing films being arranged substantially orthogonally to one another.

32. The back light module as recited in claim 29, wherein the incidence side of the diffuser produces a substantially lambertian distribution.

33. The back light module as recited in claim 29, wherein the opposing side of the second diffuser at least partially transmits light toward a back side of the second diffuser.

34. A flat panel apparatus, comprising:

a flat-panel display; and

a back light module;

the back light module comprising:

a) a diffuser having an incidence side and an output side;

b) a brightness enhancing film having an incidence side and an output side, the incidence side of the brightness enhancing film being faced toward the output side of the diffuser; and

c) a second diffuser having an opposing side that is disposed at a predetermined distance from the incidence side of the diffuser;

wherein the second diffuser produces a substantially lambertian distribution; and

wherein the incidence side of the diffuser at least partially transmits light toward the flat-panel display through the brightness enhancing film and at least partially reflects light transmitted from the output side of the diffuser back toward the flat-panel display through the brightness enhancing film, and the opposing side of the second diffuser at least partially reflects light toward the diffuser.

35. The flat panel apparatus as recited in claim 34, wherein the output side of the brightness enhancing film at least partially reflects light transmitted by the diffuser back toward the diffuser.

36. The flat panel apparatus as recited in claim 35, further comprising another brightness enhancing film, the brightness enhancing films being arranged substantially orthogonally to one another.

37. The flat panel apparatus as recited in claim 34, wherein the incidence side of the diffuser produces a substantially lambertian distribution.

38. The flat panel apparatus as recited in claim 34, wherein the opposing side of the second diffuser at least partially transmits light toward a back side of the second diffuser.

39. A back light module comprising:

a diffuser having an incidence side and an output side;

a brightness enhancing film having an incidence side and an output side, the incidence side of the brightness enhancing film being faced toward the output side of the diffuser; and

a second diffuser having an opposing side that is disposed at a predetermined distance from the incidence side of the diffuser;

wherein the incidence side of the diffuser at least partially transmits light toward the brightness enhancing film, the opposing side of the second diffuser at least partially reflects light toward the diffuser and the second diffuser produces a substantially lambertian distribution.

40. The back light module as recited in claim 39, wherein the incidence side of the diffuser at least partially reflects light transmitted from the output side of the diffuser back toward the brightness enhancing film.

41. A flat panel apparatus, comprising:

a flat-panel display; and

a back light module;

the back light module comprising:

a) a diffuser having an incidence side and an output side;

b) a brightness enhancing film having an incidence side and an output side, the incidence side of the brightness enhancing film being faced toward the output side of the diffuser; and

c) a second diffuser having an opposing side that is disposed at a predetermined distance from the incidence side of the diffuser;

wherein the incidence side of the diffuser at least partially transmits light toward the flat-panel display through the brightness enhancing film, the opposing side of the diffuser at least partially reflects light toward the diffuser and the second diffuser produces a substantially lambertian distribution.

42. The flat panel apparatus as recited in claim 41, wherein the incidence side of the diffuser at least partially reflects light transmitted from the output side of the diffuser back toward the flat-panel display through the brightness enhancing film.