CN-114556201-B - Backlight unit for backlight display

Abstract

The backlight unit includes a light emitting diode array, at least two optical films over the light emitting diode array, and a pair of brightness enhancement films over the at least two optical films. Most of the optical films are spectroscopic optical films having a plurality of spectroscopic microstructures on at least one surface thereof.

Inventors

• K.L. Walker
• SHEN BING
• M. K. Pupo

Assignees

• 亮视技术公司

Dates

Publication Date

20260508

Application Date

20200909

Priority Date

20190911

Claims (20)

1. 1. A backlight unit, comprising: an array of light emitting diodes; a lower optical film stack located over the light emitting diode array; a color conversion layer located over the lower optical film stack; An upper optical film stack located above the color conversion layer, wherein the upper optical film stack includes a pair of crossed dichroic optical films, one of the pair of crossed dichroic optical films oriented 90 ° relative to the other of the pair of crossed dichroic optical films, and A pair of brightness enhancement films over the upper optical film stack, Wherein a majority of the lower optical film stack is a spectroscopic optical film having a plurality of spectroscopic microstructures on at least one surface thereof, and wherein the spectroscopic microstructures are configured such that when a collimated light beam is directed to the microstructures on-axis, the collimated light beam is split into two or more light beams having regions of lower relative intensity on-axis.
2. 2. The backlight unit of claim 1, wherein the lower stack of optical films all has the plurality of light splitting microstructures on at least one surface thereof.
3. 3. The backlight unit of claim 1, wherein the color conversion layer is located over at least one light splitting optical film.
4. 4. The backlight unit of claim 1, wherein the color conversion layer has at least one surface comprising a plurality of light splitting microstructures.
5. 5. The backlight unit of claim 1, wherein the lower optical film stack comprises a first light splitting optical film comprising a plurality of first parallel linear prisms extending along a first direction on a first side thereof and a plurality of first elliptical columnar structures extending along a second direction on a second side thereof, the second direction being substantially orthogonal to the first direction, wherein the first side faces the array of light emitting diodes.
6. 6. The backlight unit of claim 5, wherein the lower optical film stack comprises a second light splitting optical film located above the first light splitting optical film, the second light splitting optical film comprising a plurality of second parallel linear prisms extending substantially along a first direction on a first side thereof and a plurality of second elliptical columnar structures extending along a second direction on a second side thereof, wherein a first side of the second light splitting optical film faces a second side of the first light splitting optical film.
7. 7. The backlight unit of claim 6, wherein the lower optical film stack comprises a third light splitting optical film located above the second light splitting optical film, the third light splitting optical film comprising a plurality of third parallel linear prisms extending substantially along a second direction on a first side thereof.
8. 8. The backlight unit of claim 7, wherein the third light splitting optical film further comprises a plurality of microstructures on a second side thereof.
9. 9. The backlight unit of claim 8, wherein a second side of the third light-splitting optical film faces a second side of the second light-splitting optical film.
10. 10. The backlight unit of claim 1, wherein at least one of the lower stacks of optical films is a first light splitting optical film comprising a plurality of first parallel linear prisms extending along a first direction on a first side thereof and a plurality of second parallel linear prisms extending along the first direction on a second side thereof.
11. 11. The backlight unit of claim 10, wherein at least one of the lower stacks of optical films is a second light splitting optical film comprising a plurality of first parallel linear prisms extending along the first direction on a first side thereof and a plurality of second parallel linear prisms extending along the first direction on a second side thereof.
12. 12. The backlight unit of claim 10, wherein at least one of the lower stacks of optical films is a second light splitting optical film comprising a plurality of first parallel linear prisms on a first side thereof extending along a second direction substantially orthogonal to the first direction, and a plurality of second parallel linear prisms on a second side thereof extending along the second direction.
13. 13. The backlight unit of claim 1, wherein at least one of the lower stacks of optical films is a first light splitting optical film comprising a plurality of first parallel linear prisms extending along a first direction on a first side thereof and a plurality of second parallel linear prisms extending along a second direction substantially orthogonal to the first direction on a second side thereof.
14. 14. The backlight unit of claim 1, wherein two of the lower stacks of optical films are light splitting optical films, each light splitting optical film comprising a plurality of microstructures on a first side thereof and a plurality of parallel linear prisms extending along a first direction on a second side thereof, wherein each microstructure has the shape of a rectangular pyramid.
15. 15. The backlight unit of claim 1, wherein three of the lower stacks of optical films are light splitting optical films, each light splitting optical film comprising a plurality of microstructures on a first side thereof and a plurality of parallel linear prisms extending along a first direction on a second side thereof, wherein each microstructure has the shape of a rectangular pyramid.
16. 16. A backlight unit, comprising: an array of light emitting diodes; A lower optical film stack positioned above the light emitting diode array and configured to receive light emitted by the light emitting diode array, the lower optical film stack comprising A first light splitting optical film comprising a plurality of first light splitting microstructures on a first side thereof facing the light emitting diode array, the plurality of first light splitting microstructures being constructed and arranged to split light received from the light emitting diode array, and A second light splitting optical film located above the first light splitting optical film and including a plurality of second light splitting microstructures on a first side thereof facing the first light splitting optical film, the plurality of second light splitting microstructures being constructed and arranged to split light received from the first light splitting optical film, Wherein the first and second light splitting microstructures are configured such that when the collimated light beam is directed to the microstructures on the axis, the collimated light beam is split into two or more light beams having regions of lower relative intensity on the axis; A color conversion layer located above the lower optical film stack and configured to receive light from the lower optical film stack; an upper optical film stack positioned above the color conversion layer and configured to receive light from the color conversion layer, wherein the upper optical film stack includes a pair of crossed dichroic optical films, one of the pair of crossed dichroic optical films oriented 90 ° relative to the other of the pair of crossed dichroic optical films, and A pair of brightness enhancement films positioned above the upper optical film stack and configured to receive light from the upper optical film stack.
17. 17. The backlight unit of claim 16, wherein the plurality of first light splitting microstructures comprises a plurality of first parallel linear prisms and the plurality of second light splitting microstructures comprises a plurality of second parallel linear prisms oriented orthogonal to the plurality of first parallel linear prisms.
18. 18. The backlight unit of claim 17, wherein the first light splitting optical film further comprises a plurality of first random coarse microstructures on a second side thereof, and the second light splitting optical film further comprises a plurality of second random coarse microstructures on a second side thereof.
19. 19. The backlight unit of claim 16, wherein the lower stack of optical films further comprises a third optical film positioned over the second light splitting optical film.
20. 20. The backlight unit of claim 19, wherein the third optical film comprises a plurality of microstructures facing the second light splitting optical film.

Description

Backlight unit for backlight display Cross Reference to Related Applications The present application claims the priority benefits of U.S. provisional patent application Ser. No.62/898,693, filed on day 9, month 11, 2019, U.S. provisional patent application Ser. No.62/929,309, and U.S. provisional patent application Ser. No.63/023,618, filed on day 5, month 12, 2020, which are all incorporated herein by reference in their entireties. Technical Field The present invention relates generally to backlight units for backlight displays, and more particularly to backlight displays having Light Emitting Diode (LED) light sources. Background In pursuit of improved image quality, liquid Crystal Displays (LCDs) increasingly use a backlight unit architecture 100, as schematically illustrated in fig. 1, which includes an array 110 of individual short wavelength (blue) LEDs 112. Fig. 2A and 2B illustrate typical intensity distribution as a function of angle of light emitted from a single LED as measured by a goniophotometer. As shown, the LED light source approximates a Lambertian (Lambertian) light source that emits a light distribution that is substantially symmetrical about a nadir, with the highest light intensity at the nadir. Returning to fig. 1, a series of films may be used to spread or diffuse the light emitted from the blue LEDs 112 so that the backlight unit 100 may deliver more uniform light to an LCD panel (not shown) containing liquid crystals above the backlight unit 100. As shown, the backlight unit 100 generally includes a diffuser film 120, which may be a volume diffuser or a circular diffuser, a color conversion layer 130 that converts some of the blue light emitted by the LEDs 110 into green and red light using, for example, quantum dots or phosphor materials, a diffuser film 140, which may be a volume diffuser or a circular diffuser created by a random textured surface, configured to spread or diffuse the light exiting the color conversion layer 130, and two Brightness Enhancement Films (BEFs) 150, 160, which are generally prismatic films that are rotated approximately 90 degrees relative to one another. An additional film may be provided in the backlight unit 100 for improving the overall uniformity and brightness of light delivered to the LCD panel. In some backlight units, white LEDs may be used without a color conversion layer. When the LEDs 112 are arranged in an array, such as the array 110 shown in fig. 3, it is desirable to hide the individual LEDs 112 and present bright and uniform light to the LCD panel. As described above, one way to achieve this goal is to include one or more diffusers, such as diffuser films 120, in the backlight unit 100 to diffuse, spread, or blur the light beam emitted by the LEDs 112. Fig. 4 schematically illustrates such diffusion of light emitted by a single LED 112, wherein darker shades of gray represent brighter light than lighter shades of gray. This diffusion may also reduce the average energy of the light. In addition, electronic devices including LCDs are becoming thinner and thinner. Accordingly, the backlight units of such displays also become thinner and thinner, which presents another challenge for managing the light emitted by the LEDs 112 in an efficient manner. For example, when the diffuser film 120 is placed over the array 110 of LEDs 112, as schematically shown in fig. 5A, the individual light spots emitted by the LEDs are diffused such that light from adjacent LEDs 112 with less intensity begins to overlap to create a light region with higher intensity. If the thickness of the diffuser film 120 is increased, which may be undesirable for a thinner backlight unit 100, the individual spots may spread farther and provide better light uniformity, but still present brighter and darker areas, as schematically shown in fig. 5B. It is desirable to have a backlight unit 100 for an LCD display that has an array 110 of blue LEDs 112 and a thin profile, but still delivers bright and uniform light to the LCD panel while effectively hiding the individual LEDs 112. Disclosure of Invention According to an embodiment of the present invention, there is provided a backlight unit including a light emitting diode array, at least two optical films located over the light emitting diode array, and a pair of brightness enhancement films located over the at least two optical films. The majority of the at least two optical films are spectroscopic optical films having a plurality of spectroscopic microstructures on at least one surface thereof. In an embodiment, the at least two optical films all have the plurality of spectroscopic microstructures on at least one surface thereof. In an embodiment, the backlight unit includes a color conversion layer over the light emitting diode array and under the pair of brightness enhancement films. In an embodiment, the color conversion layer is located over the at least one light splitting optical film. In an embodiment, the color convers