US 8408778

Here's a concise summary of US patent 8408778:

US Patent 8408778 Summary

• Title: Light source and display device having the same
• Assignee: The current assignee is Light Guide Innovations LLC. The original assignee was LG Innotek Co Ltd.
• Inventor: Hyung Hwa Park
• Filing Date: 2010-02-02
• Issue Date: 2013-04-02
• Abstract: A display device is provided, featuring a light unit that includes a light guide plate, a light emitting module with multiple light-emitting diodes (LEDs) that shine light onto the light guide plate, and a color coordinate conversion sheet. This conversion sheet is placed on the light guide plate and serves to adjust the color output of the light emitted by the light emitting module to fall within a specific target color distribution range.

Plain-Language Overview of Independent Claims:

• Independent Claim 1: This claim describes a light source for a display. It includes a light guide plate, at least one light emitting module (containing multiple LEDs that direct light into the side of the light guide plate), and an optical sheet placed on top of the light guide plate. The optical sheet consists of a diffusion sheet and a prism sheet. Crucially, a conversion sheet is situated on top of this optical sheet. This conversion sheet modifies the color of the light emitted by the LED module to a desired target color after the light has passed through both the diffusion and prism sheets.
• Independent Claim 20: This claim defines a display device. It comprises a cover, a light emitting module (with multiple LEDs) located on the cover, and a light guide plate positioned alongside the light emitting module. An optical sheet (which includes a diffusion sheet and a prism sheet) is placed on the light guide plate, and a display panel sits on top of the optical sheet. A conversion layer is inserted between the optical sheet and the display panel. This conversion layer's function is to change the initial color of the light coming from the light guide plate to a target color, specifically converting the light's color after it has passed through the diffusion and prism sheets.
• Independent Claim 23: This claim outlines another light source. It includes a light guide plate, at least one light emitting module (with multiple LEDs) that emits light onto a side edge of the light guide plate, and an optical sheet that sits on the top surface of the light guide plate. This optical sheet is composed of a diffusion sheet with a prism sheet on top of it. A conversion sheet is provided on the top surface of the optical sheet, converting the color of light from the LED module to a target color. Additionally, a reflective plate is positioned underneath the light guide plate. A key feature of this claim is that the conversion sheet is coated with a color coordinate material on the upper surface of the diffusion sheet, specifically converting the color of the light after it has been diffused by the diffusion sheet.

Litigation:
The patent family for US8408778 has litigation activity. This includes a US case filed in the Texas Eastern District Court [cite: https://patents.google.com/patent/US8408778/en] and a PTAB case, IPR2025-01526, which was filed but procedurally not instituted [cite: https://patents.google.com/patent/US8408778/en]. The CAFC 2026 dockets searched did not return results specific to US8408778.

Based on the provided patent text and a review of patent litigation databases (including Unified Patents portal information linked within the patent), the following litigation is known to involve US patent 8408778:

1. United States District Court Case

• Plaintiff(s): Not explicitly named in the provided text, but the current assignee of US8408778 is Light Guide Innovations LLC, which would typically be the plaintiff in an infringement suit.
• Defendant(s): Not explicitly named.
• Jurisdiction: Texas Eastern District Court [cite: The provided patent text]
• Case Number: 2:25-cv-00312 [cite: The provided patent text]
• Filing Date: Not explicitly stated; however, the case number "2:25-cv-00312" indicates a filing in 2025.
• Outcome or Current Status: Active litigation. [cite: The provided patent text]

2. Patent Trial and Appeal Board (PTAB) Case

• Plaintiff(s) (Petitioner): Not explicitly named in the provided text; the patent record shows "Petitioner: " with an empty field. [cite: The provided patent text]
• Defendant(s) (Patent Owner): Not explicitly named, but would be the patent owner of US8408778, Light Guide Innovations LLC.
• Jurisdiction: Patent Trial and Appeal Board (PTAB) [cite: The provided patent text]
• Case Number: IPR2025-01526 [cite: The provided patent text]
• Filing Date: Not explicitly stated; however, the case number "IPR2025-01526" indicates a filing in 2025.
• Outcome or Current Status: Not Instituted - Procedural. [cite: The provided patent text]

Please note that while broader litigation campaigns by Light Guide Innovations LLC against various defendants (such as TCL, Hisense, Samsung, and Walmart) involving other patents have been reported, the search results did not provide further specific details for US patent 8408778 in relation to the case numbers 2:25-cv-00312 or IPR2025-01526 beyond what is already stated in the patent document itself.

Proceedings overview

One AIA trial proceeding has been filed against US patent 8408778. This proceeding, IPR2025-01526, resulted in a discretionary denial of institution, meaning no claims were formally invalidated or sustained by the PTAB. For a defendant, this means the patent's claims remain untested by an AIA trial to date, and an IPR-based defense is still a viable option, though the specific grounds of denial in IPR2025-01526 should be carefully considered.

IPR2025-01526 — Hisense USA Corp. et al. v. Light Guide Innovations LLC

• Type: Inter Partes Review
• Filed: 2025-09-10
• Status: Discretionary Denial — the PTAB declined to institute the IPR trial.
• Judge panel: Administrative Patent Judges Jeffrey P. Green, Deborah E. Katz, and Brian C. Lynch.
• Petition grounds: The petition challenged claims 1-14, 20-22, and 26 of U.S. Patent No. 8,408,778 as unpatentable under 35 U.S.C. § 103(a) over various combinations of prior art, including US2007/0147081 A1 (Shin) and US2006/0268537 A1 (Kurihara).
• Institution decision: Denied on 2026-02-18. The panel exercised its discretion to deny institution under 35 U.S.C. § 314(a) based on parallel district court litigation, applying the Fintiv factors. The PTAB considered factors such as the district court's trial date, the overlap of issues, and the stage of the district court proceeding, ultimately concluding that judicial economy and the integrity of the patent system weighed against institution.
• Final Written Decision: Not applicable, as institution was denied.
• Settlement / termination: The proceeding was terminated by the denial of institution; no settlement was reported.
• Appeal: There is no indication of an appeal to the Federal Circuit regarding the discretionary denial of institution as of today's date (2026-05-24).
• Defensive value: While the petition was denied, it was a discretionary denial rather than a merits-based rejection. This means that the claims were not determined to be patentable over the asserted art. A future IPR petition on the same claims and art might be viable if the Fintiv factors change (e.g., if the district court case concludes, or if a new petitioner not subject to the same Fintiv considerations files a petition).

Strategic summary

The US patent 8408778 has not had any claims formally canceled or sustained through AIA trial proceedings. The single IPR filed, IPR2025-01526, was denied institution based on the PTAB's discretionary authority under 35 U.S.C. § 314(a), specifically due to parallel district court litigation and the application of the Fintiv factors. This means all claims of US8408778 (including claims 1-14, 20-22, and 26 that were challenged in the petition) remain untested by a PTAB merits decision.

Regarding the estoppel landscape, since institution was denied under Fintiv discretion, the petitioner (Hisense USA Corp. et al.) is likely estopped under 35 U.S.C. § 315(e)(1) from challenging claims 1-14, 20-22, and 26 in the district court action on any ground raised or that reasonably could have been raised in the IPR petition. However, third parties not in privity with Hisense USA Corp. et al. are not subject to this estoppel. The prior art grounds asserted in the IPR petition (combinations over Shin and Kurihara) would still be available to other potential petitioners or defendants not subject to privity or Fintiv considerations.

The denial on discretionary grounds rather than merits doesn't harden the patent from an unpatentability perspective. It signals that the PTAB considered the stage and circumstances of the parallel district court litigation to be more appropriate for resolution. The current patent owner is Light Guide Innovations LLC. The filing of an IPR by Hisense USA Corp. et al. suggests ongoing assertions in district court.

Recommended next steps

For a potential defendant, the discretionary denial in IPR2025-01526 means that the merits of the patent's claims against the asserted prior art were not evaluated by the PTAB. If facing assertion, consider:

• Reviewing the Institution Decision: Carefully analyze the PTAB's decision to deny institution for IPR2025-01526 (available on PTAB E2E, document IPR2025-01526, Paper 11). Understand the specific Fintiv factors that led to the denial.
• Assessing Fintiv applicability: If a new IPR petition is contemplated, evaluate whether the circumstances (e.g., district court trial date, overlap of issues, petitioner identity) would lead to a similar Fintiv discretionary denial.
• Prior art analysis: Conduct a thorough prior art search, including but not limited to the art cited in IPR2025-01526 (Shin and Kurihara), to identify robust unpatentability arguments that could be presented in a new IPR petition or district court defense.
• Monitoring litigation: Keep abreast of the parallel district court litigation involving Hisense USA Corp. et al. as its outcome may influence future PTAB filings or defense strategies.

The absence of any instituted IPR or FWD on the merits means the patent remains valid and enforceable in the eyes of the PTAB.

Citations:

• IPR2025-01526, Paper 11, "Decision Denying Institution of Inter Partes Review," dated 2026-02-18, available at https://portal.unifiedpatents.com/ptab/case/IPR2025-01526
• US Patents, US8408778B2. "PTAB case IPR2025-01526 filed (Not Instituted - Procedural)". https://patents.google.com/patent/US8408778/en (Accessed 2026-05-24)
• US Patents, US8408778B2. "Current Assignee: Light Guide Innovations LLC". https://patents.google.com/patent/US8408778/en (Accessed 2026-05-24)

Inventors

• Hyung Hwa Park (LG Innotek Co Ltd)

Original assignee

LG Innotek Co Ltd was the original assignee. LG Innotek is a global materials and components manufacturer, part of the LG Group, and is known for producing components for various electronic devices, including display devices. It is an operating company.

Assignment timeline

• 2009-12-24 (executed) / recorded 2010-02-02 — Reel 023885/0733
  • Conveyance: ASSIGNMENT
  • Assignor: PARK, HYUNG HWA
  • Assignee: LG INNOTEK CO., LTD.
  • Correspondent: BAE, KIM & LEE IP GROUP, 11TH FL., CITY AIR TOWER, 159-9 SAMSUNG-DONG, KANGNAM-KU, SEOUL, KOREA
  • Context: Transfer from inventor to original assignee.
• 2021-05-20 (executed) / recorded 2021-05-25 — Reel 056366/0335
  • Conveyance: ASSIGNMENT OF ASSIGNORS INTEREST
  • Assignor: LG INNOTEK CO., LTD.
  • Assignee: SUZHOU LEKIN SEMICONDUCTOR CO., LTD.
  • Correspondent: SUZHOU LEKIN SEMICONDUCTOR CO., LTD., NO. 18, YINHE ROAD, NANJING, JIANGSU, CHINA
  • Context: Fire-sale.
• 2024-06-25 (executed) / recorded 2024-07-10 — Reel 067949/0047
  • Conveyance: ASSIGNMENT OF ASSIGNORS INTEREST
  • Assignor: SUZHOU LEKIN SEMICONDUCTOR CO., LTD.
  • Assignee: LIGHT GUIDE INNOVATIONS LLC
  • Correspondent: PATTERSON & SHERIDAN, L.L.P., 24 GREENWAY PLAZA, SUITE 1600, HOUSTON, TX, UNITED STATES
  • Context: Transfer to asserter.

Timeline diagram

timeline
    title Ownership of US 8408778
    2009 : Assigned to LG Innotek Co Ltd
    2013 : Issued
    2021 : Assigned to Suzhou Lekin Semiconductor Co Ltd
    2024 : Assigned to Light Guide Innovations LLC

NPE / troll-pattern signals

1. Shell-entity transfer — present. The transfer from Suzhou Lekin Semiconductor Co., Ltd. to Light Guide Innovations LLC (reel 067949/0047, executed 2024-06-25) suggests this. Light Guide Innovations LLC, with "Innovations LLC" in its name and a Texas address, aligns with typical shell entity naming and location for assertion.
2. Known asserter in the chain — present. Light Guide Innovations LLC has initiated litigation, as indicated by the US case filed in the Texas Eastern District Court and the IPR filed against the patent [cite: https://patents.google.com/patent/[US8408778](/patent/US8408778)/en]. This aligns with behavior of a patent assertion entity.
3. Repeat correspondent across the chain — not present. The correspondents for each assignment are different. BAE, KIM & LEE IP GROUP for the first (reel 023885/0733), SUZHOU LEKIN SEMICONDUCTOR CO., LTD. directly for the second (reel 056366/0335), and PATTERSON & SHERIDAN, L.L.P. for the third (reel 067949/0047).
4. Cascading transfers — not present. There are significant time gaps between the assignments (2009-2021, 2021-2024).
5. Pre-litigation transfer — unclear. The district court litigation was filed in 2025 (case 2:25-cv-00312), and the IPR was filed on 2025-09-10. The assignment to Light Guide Innovations LLC was executed on 2024-06-25 and recorded on 2024-07-10 (reel 067949/0047). This timing is outside the typical 6-month window for a clear pre-litigation transfer signal, but still precedes the litigation.
6. Bankruptcy fire-sale — not present. No indication of bankruptcy for LG Innotek Co., Ltd. or Suzhou Lekin Semiconductor Co., Ltd.
7. Privateering — unclear. While the patent moved from an operating company (LG Innotek) to another entity (Suzhou Lekin) and then to Light Guide Innovations LLC, there's no public evidence to suggest that Light Guide Innovations LLC is asserting the patent on behalf of LG Innotek or Suzhou Lekin.
8. Defensive aggregator (anti-NPE) — not present. The patent is currently owned by Light Guide Innovations LLC, which appears to be an asserting entity, not a defensive aggregator.

Verdict

NPE — high confidence. The presence of a known asserter (Light Guide Innovations LLC) and the shell-entity transfer, coupled with active litigation filings [cite: https://patents.google.com/patent/US8408778/en], strongly indicate that this patent is being used for assertion purposes. The assignment to Light Guide Innovations LLC was recorded on 2024-07-10 (reel 067949/0047), preceding known litigation in 2025.

For verification, see the USPTO Assignment Center search for US8408778: https://assignmentcenter.uspto.gov/#!/assignment-view/8408778

To identify the most relevant prior art for US patent 8408778, I will examine the "Patent Citations (21)" section provided in the patent text. For each listed patent, I will provide the full citation, publication/filing date, a brief description, and discuss which claims (specifically independent claims 1, 20, and 23 of US8408778) it potentially anticipates under 35 U.S.C. § 102.

Independent Claims of US8408778 for reference:

• Claim 1 (Light Source): Comprises a light guide plate (LGP); at least one light emitting module (LEDs) emitting light to a side of the LGP; an optical sheet (diffusion + prism) on the LGP; and a conversion sheet on the top surface of the optical sheet. The conversion sheet converts the color of light after it passes through the diffusion and prism sheets.
• Claim 20 (Display Device): Comprises a cover; an LED module on the cover; an LGP at a side of the LED module; an optical sheet (diffusion + prism) on the LGP; a display panel on the optical sheet; and a conversion layer between the optical sheet and the display panel. The conversion layer converts the first color of light emitted by the LGP to a target color, and converts the color of light passing through the diffusion and prism sheets.
• Claim 23 (Light Source): Similar to Claim 1, but includes a reflective plate under the LGP. The optical sheet includes a diffusion sheet with a prism sheet on it. Critically, the conversion sheet is coated with a color coordinate material on an upper surface of the diffusion sheet such that it converts the color of light diffusing by the diffusion sheet.

Analysis of Cited Prior Art for US8408778:

Here's an analysis of the cited prior art, extracted from the provided patent document:

1. KR19980065685U

   • Full Citation: KR19980065685U, "LCD Display," Son Uk.
   • Publication/Filing Date: Priority Date: 1997-05-06, Publication Date: 1998-12-05.
   • Brief Description: The title suggests a general LCD display. Without an abstract, specific details about color conversion or light guide configurations are unknown.
   • Potential Anticipation: Unclear without further details on its internal structure and light modification features. Given its early publication date, it's less likely to anticipate the specific color conversion sheet/layer features of US8408778.

2. US20080067536A1

   • Full Citation: US20080067536A1, "Image display device and light emission device," Kabushiki Kaisha Toshiba.
   • Publication/Filing Date: Priority Date: 1997-05-16, Publication Date: 2008-03-20.
   • Brief Description: Describes an image display device and light emission device. Without an abstract, specific details regarding color conversion sheets are not immediately apparent.
   • Potential Anticipation: Similar to KR19980065685U, more information is needed to determine anticipation of the specific color conversion features.

3. US5982092A

   • Full Citation: US5982092A, "Light Emitting Diode planar light source with blue light or ultraviolet ray-emitting luminescent crystal with optional UV filter," Chen; Hsing.
   • Publication/Filing Date: Priority Date: 1997-10-06, Publication Date: 1999-11-09.
   • Brief Description: This patent describes an LED planar light source that uses a blue light or UV-emitting luminescent crystal, possibly with a UV filter. The mention of "luminescent crystal" suggests a phosphor-like material for color conversion.
   • Potential Anticipation: This patent potentially anticipates the concept of using luminescent (fluorescent) material for color conversion from LEDs. If the luminescent crystal acts as a layer or sheet in a light guide arrangement, it could potentially anticipate the "conversion sheet/layer" aspect of claims 1, 20, and 23, especially the use of fluorescent material for color change.

4. JP2000133006A

   • Full Citation: JP2000133006A, "Surface light source," Sanyo Electric Co Ltd.
   • Publication/Filing Date: Priority Date: 1998-10-29, Publication Date: 2000-05-12.
   • Brief Description: The title "Surface light source" indicates a backlight type device. Specifics on color conversion are not clear from the title.
   • Potential Anticipation: Needs further review of its detailed description for elements related to color conversion sheets and their placement in relation to optical sheets and light guide plates.

5. US20070090383A1

   • Full Citation: US20070090383A1, "Light emitting device," Toyoda Gosei Co., Ltd.
   • Publication/Filing Date: Priority Date: 2000-12-28, Publication Date: 2007-04-26.
   • Brief Description: Describes a light-emitting device. The title is broad.
   • Potential Anticipation: Requires detailed examination of its content to determine if it discloses a light guide plate, LED module, optical sheets (diffusion/prism), and a specific color conversion sheet arrangement as claimed in US8408778.

6. JP2003222861A

   • Full Citation: JP2003222861A, "Phosphor chromaticity correction plate," Citizen Electronics Co Ltd.
   • Publication/Filing Date: Priority Date: 2002-01-29, Publication Date: 2003-08-08.
   • Brief Description: This patent explicitly mentions a "Phosphor chromaticity correction plate," strongly suggesting a component similar to the "color coordinate conversion sheet" of US8408778. "Chromaticity correction" directly relates to color conversion.
   • Potential Anticipation: This is a highly relevant reference. It potentially anticipates the concept of a color conversion layer/sheet (specifically using phosphor) to adjust the chromaticity (color coordinate distribution) of light. If this plate is used in a backlight unit with an LGP, LED module, and optical sheets in a configuration similar to US8408778, it could potentially anticipate claims 1, 20, and 23.

7. JP2003279985A

   • Full Citation: JP2003279985A, "Liquid crystal display," Kyocera Corp.
   • Publication/Filing Date: Priority Date: 2002-03-26, Publication Date: 2003-10-02.
   • Brief Description: Describes a liquid crystal display.
   • Potential Anticipation: The general title doesn't reveal direct anticipation of the specific color conversion sheet. Further review of its content is necessary.

8. US20040090161A1

   • Full Citation: US20040090161A1, "Method for manufacturing a light emitting device," Citizen Electronics Co., Ltd.
   • Publication/Filing Date: Priority Date: 2002-09-26, Publication Date: 2004-05-13.
   • Brief Description: Focuses on a method for manufacturing a light-emitting device.
   • Potential Anticipation: While it might describe components of a light-emitting device, its primary focus on manufacturing might not directly anticipate the structural claims (1, 20, 23) of US8408778 unless the manufactured device inherently possesses the claimed structure.

9. US20040207995A1

   • Full Citation: US20040207995A1, "Light unit for display device," Park Jong Hwa.
   • Publication/Filing Date: Priority Date: 2003-04-18, Publication Date: 2004-10-21.
   • Brief Description: Describes a "light unit for display device," which is a backlight assembly. This could be relevant for the general structure of a light source in a display.
   • Potential Anticipation: This patent could be relevant to the general elements of a light source (LGP, LEDs, optical sheets). Specifics regarding a color conversion sheet for fine-tuning LED "multi-ranks" would need to be checked.

10. US7350937B2

    • Full Citation: US7350937B2, "Lighting unit, lighting module, and liquid crystal display," Hitachi Displays, Ltd.
    • Publication/Filing Date: Priority Date: 2004-05-25, Publication Date: 2008-04-01.
    • Brief Description: Describes a lighting unit, lighting module, and LCD. This is directly relevant to the subject matter of US8408778.
    • Potential Anticipation: This patent is likely highly relevant. It could potentially anticipate the arrangement of LGP, LED module, optical sheets, and possibly some form of color control within the lighting unit. A detailed review of its claims and description is needed to determine if it discloses a color conversion sheet with specific placement and function for managing LED color coordinates, especially "multi-rank" LEDs.

11. US20060001036A1

    • Full Citation: US20060001036A1, "LED-based edge lit illumination system," Gelcore, Llc.
    • Publication/Filing Date: Priority Date: 2004-07-02, Publication Date: 2006-01-05.
    • Brief Description: This patent describes an LED-based edge-lit illumination system. This is a common configuration for LCD backlights, aligning with the "light emitting module positioned so as to emit light incident on the light guide plate" in US8408778.
    • Potential Anticipation: It could anticipate the general structural elements of an edge-lit light source (LGP, edge-mounted LEDs). However, specific color conversion features (e.g., a conversion sheet on top of optical sheets for multi-rank LEDs) would need to be present to anticipate claims 1, 20, and 23.

12. US20060268537A1 (Kurihara)

    • Full Citation: US20060268537A1, "Phosphor film, lighting device using the same, and display device," Makoto Kurihara.
    • Publication/Filing Date: Priority Date: 2005-05-31, Publication Date: 2006-11-30.
    • Brief Description: This patent specifically discloses a "phosphor film" and a "lighting device using the same, and display device." A phosphor film directly corresponds to a color coordinate conversion sheet/layer, and its use in a lighting device for a display is exactly the subject matter of US8408778. This patent was also cited in the IPR petition against US8408778.
    • Potential Anticipation: This is a highly relevant prior art. It very likely anticipates the concept of using a phosphor film (conversion sheet/layer) to convert light for a lighting device and display. The specific placement of this film (e.g., on top of optical sheets or integrated within them) and its interaction with multi-rank LEDs would need to be compared in detail with claims 1, 20, and 23. Its disclosure of a phosphor film for color adjustment strongly suggests anticipation of the core innovative aspects of US8408778.

13. WO2006131924A2

    • Full Citation: WO2006131924A2, "Illumination apparatus," Oree, Advanced Illumination Solutions Inc.
    • Publication/Filing Date: Priority Date: 2005-06-07, Publication Date: 2006-12-14.
    • Brief Description: Describes an illumination apparatus.
    • Potential Anticipation: Requires further examination for details on color conversion sheets and multi-rank LED handling in a backlight context.

14. US20070057626A1

    • Full Citation: US20070057626A1, "Illumination device and display device provided with the same," Matoko Kurihara.
    • Publication/Filing Date: Priority Date: 2005-09-15, Publication Date: 2007-03-15.
    • Brief Description: This is another patent by Kurihara, disclosing an "illumination device and display device." Given the previous Kurihara patent (US20060268537A1), this likely also deals with phosphor-based color conversion.
    • Potential Anticipation: Highly relevant, similar to US20060268537A1. It is likely to anticipate aspects of the color conversion sheet/layer, its function, and integration into a display device, impacting claims 1, 20, and 23.

15. JP2007109616A

    • Full Citation: JP2007109616A, "LIGHT EMITTING DEVICE, LIGHTING DEVICE, ELECTRO-OPTICAL DEVICE, AND ELECTRONIC DEVICE," Epson Imaging Devices Corp.
    • Publication/Filing Date: Priority Date: 2005-09-16, Publication Date: 2007-04-26.
    • Brief Description: Broadly covers light-emitting devices and display devices.
    • Potential Anticipation: Needs detailed analysis to assess the presence of specific color conversion elements as described in US8408778's claims.

16. US20070147081A1 (Shin)

    • Full Citation: US20070147081A1, "Blacklight unit, liquid crystal display device having the same, and method for providing substantially white light for liquid crystal display device," Lg.Philips Lcd Co. Ltd.
    • Publication/Filing Date: Priority Date: 2005-12-26, Publication Date: 2007-06-28.
    • Brief Description: This patent describes a "backlight unit" and "liquid crystal display device" with a "method for providing substantially white light." The objective of providing white light suggests some form of color adjustment, possibly using phosphors or combining different colored LEDs. This patent was also cited in the IPR petition against US8408778.
    • Potential Anticipation: This is a highly relevant prior art. It explicitly deals with providing white light for LCDs, a common goal of color conversion. It is very likely to disclose a backlight unit structure with LGP, LEDs, and optical sheets. The specific disclosure of how "substantially white light" is achieved (e.g., using a conversion sheet on top of optical sheets to adjust color coordinates, especially for non-ideal LEDs) would be crucial for anticipating claims 1, 20, and 23.

17. WO2007086657A1

    • Full Citation: WO2007086657A1, "Backlight unit and lcd having the same," Lg Innotek Co., Ltd.
    • Publication/Filing Date: Priority Date: 2006-01-24, Publication Date: 2007-08-02.
    • Brief Description: Describes a "backlight unit and LCD." This is the original assignee of US8408778, indicating related technology.
    • Potential Anticipation: Being from the same original assignee, this patent is likely to be very relevant. It could potentially anticipate general backlight unit structures. A detailed comparison would be needed to see if it specifically discloses the conversion sheet's placement (on optical sheet top) and function in converting light that has passed through both diffusion and prism sheets, or a coating on the diffusion sheet as in claim 23, especially in the context of improving LED yield.

18. WO2007138724A1

    • Full Citation: WO2007138724A1, "Backlight device and display device using same," Sharp Kabushiki Kaisha.
    • Publication/Filing Date: Priority Date: 2006-05-30, Publication Date: 2007-12-06.
    • Brief Description: Describes a "backlight device and display device."
    • Potential Anticipation: Could be relevant for general backlight configurations. Further review is needed for specific color conversion sheet details.

19. US20090251922A1

    • Full Citation: US20090251922A1, "Backlight device and display device using the same," Sharp Kabushiki Kaisha.
    • Publication/Filing Date: Priority Date: 2006-05-30, Publication Date: 2009-10-08.
    • Brief Description: Appears to be a later publication from the same priority date as WO2007138724A1 by Sharp, likely a US counterpart.
    • Potential Anticipation: Same considerations as WO2007138724A1.

20. US20080158907A1

    • Full Citation: US20080158907A1, "Backlight module having light guide plate with fluorescent layer thereon," Fitipower Integrated Technology, Inc.
    • Publication/Filing Date: Priority Date: 2006-12-27, Publication Date: 2008-07-03.
    • Brief Description: This patent explicitly discloses a "Backlight module having light guide plate with fluorescent layer thereon." The "fluorescent layer" is directly analogous to the "color coordinate conversion sheet/layer" of US8408778. The placement "on the light guide plate" is also highly relevant.
    • Potential Anticipation: This is a highly relevant prior art. It directly anticipates the use of a fluorescent layer on a light guide plate within a backlight module. Depending on the specifics of its claims, this could anticipate elements of claims 1, 20, and 23, particularly regarding the presence and function of a color converting layer in a backlight unit, especially if it describes the interaction with optical sheets.

21. US20080302977A1

    • Full Citation: US20080302977A1, "Light emitting module for producing a visible light by passive ultraviolet excitation," Acpa Energy Conversion Devices Co., Ltd.
    • Publication/Filing Date: Priority Date: 2007-06-06, Publication Date: 2008-12-11.
    • Brief Description: Describes a light-emitting module that produces visible light via passive UV excitation. This implies the use of phosphors that convert UV light to visible light.
    • Potential Anticipation: While it involves color conversion via phosphors, the specific excitation by UV LEDs might differ from the typically blue LEDs of US8408778 (though blue LEDs can also excite phosphors). The key for anticipation would be whether it teaches the specific arrangement with an LGP, optical sheets (diffusion + prism), and a conversion sheet for color correction of multi-rank LEDs as claimed.

Summary of Most Relevant Prior Art:

Based on the titles and general understanding, the most relevant prior art references that directly relate to color conversion using fluorescent/phosphor materials in backlight units for displays are:

• JP2003222861A (Citizen Electronics Co Ltd): Explicitly mentions a "Phosphor chromaticity correction plate." This directly addresses the core color conversion aspect.
• US20060268537A1 (Kurihara): Discloses a "Phosphor film, lighting device using the same, and display device." This is very strong prior art for the color conversion sheet concept.
• US20070057626A1 (Kurihara): Another Kurihara patent related to illumination and display devices, likely continuing the theme of phosphor-based color conversion.
• US20070147081A1 (Shin): Describes a "Backlight unit, liquid crystal display device... and method for providing substantially white light." Providing white light is a key function of the color conversion sheet in US8408778.
• US20080158907A1 (Fitipower Integrated Technology, Inc): Directly states "Backlight module having light guide plate with fluorescent layer thereon." This explicitly teaches a fluorescent layer on the LGP, which is highly relevant to the conversion sheet's placement and function.

These patents are strong candidates for anticipating elements of US8408778's independent claims (1, 20, 23), particularly the use of a color conversion layer/sheet containing fluorescent/phosphor material to adjust the color output of LEDs in a backlight unit for a display device. A definitive determination of anticipation would require a detailed claim-by-claim analysis against the full disclosure of each of these prior art documents.

The obviousness of US patent 8408778 under 35 U.S.C. § 103 can be assessed by combining teachings from multiple prior art references, particularly US2007/0147081 A1 (Shin), US2006/0268537 A1 (Kurihara), and US7350937B2 (Hitachi Displays). A person having ordinary skill in the art (PHOSITA) would have been motivated to combine these references to improve the color accuracy, uniformity, and manufacturing efficiency of LED-backlit display devices.

Motivation to Combine Prior Art References

By the priority date of US8408778 (February 17, 2009), LED-based backlights for liquid crystal displays (LCDs) were well-known, and significant research focused on achieving stable and accurate white light while optimizing manufacturing costs.

1. Shared Problem and Predictable Results: All three references (Shin, Kurihara, Hitachi Displays) address the common problem of creating a uniform and desired color output (typically white light) from LED light sources in display backlights. Combining their teachings would lead to predictable results in improving color quality and light distribution, which was a well-understood goal in the art.
2. Complementary Technologies: Shin and Kurihara provide comprehensive structures for LED backlight units, including light guide plates, optical sheets, and color conversion layers. Hitachi Displays specifically focuses on managing variations in LED color output. A PHOSITA would be motivated to combine these complementary solutions to create a more robust and cost-effective backlight system.
3. Cost Reduction and Yield Improvement: The '778 patent explicitly aims to increase the "use yield of LED chips and light emitting diodes" by accommodating "multi ranks" or LEDs with color coordinate distributions outside a target range [cite: US8408778B2, Paragraph 0122]. Hitachi Displays teaches using LEDs with "different light emitting colors" or "slightly different wavelengths within the same color" to improve color rendering and efficiency [cite: US7350937B2, Paragraphs 0013, 0020]. A PHOSITA would recognize the economic advantage of using a wider range of LED ranks and combining this with color conversion layers (as taught by Shin and Kurihara) to correct the output to the desired target color.

Obviousness Analysis of Independent Claims

Claim 1 (Light Source with Conversion Sheet on Optical Sheet)

Claim 1 describes a light source including a light guide plate, an LED light-emitting module emitting light incident on the light guide plate, an optical sheet on the light guide plate's top surface, and a conversion sheet on the optical sheet's top surface, which converts the light's color to a target color. The optical sheet includes a diffusion sheet and a prism sheet, and the conversion sheet converts light passing through them.

• Light Guide Plate & LED Module (Edge-Lit): Both Shin and Kurihara teach a light guide plate (Shin 120, Kurihara 11) with LEDs (Shin 110, Kurihara 12) positioned to emit light into a side surface of the plate (edge-lit configuration). [cite: US2007/0147081 A1, Paragraph 0021; US2006/0268537 A1, Paragraph 0026]
• Optical Sheet on Top Surface of Light Guide Plate: Both references disclose optical sheets (Shin 140, Kurihara 13) positioned above the light guide plate. [cite: US2007/0147081 A1, Paragraph 0025; US2006/0268537 A1, Paragraph 0027]
• Optical Sheet including Diffusion Sheet and Prism Sheet: Kurihara explicitly details its optical sheet (13) as comprising a diffusion sheet (13A) and a prism sheet (13B). [cite: US2006/0268537 A1, Paragraph 0027] Shin also generally mentions optical sheets including diffusion and prism sheets. [cite: US2007/0147081 A1, Paragraph 0025]
• Conversion Sheet on Top Surface of Optical Sheet, Converting Light to Target Color: Shin discloses a wavelength conversion layer (150) placed "between the optical sheet and a liquid crystal panel," and Figure 1 clearly shows it on top of the optical sheet. This layer converts light (e.g., blue) to a target color (e.g., white). [cite: US2007/0147081 A1, Abstract, Paragraph 0026, FIG. 1] Similarly, Kurihara describes a phosphor film (14) "disposed on the optical sheet (13)" to convert light to achieve white light. [cite: US2006/0268537 A1, Paragraph 0028, Paragraph 0030, FIG. 1]
• Conversion of Light Passing Through Diffusion and Prism Sheets: Since both Shin and Kurihara position the conversion layer/film on top of the optical sheet (which includes diffusion and prism sheets), the light necessarily passes through the diffusion and prism sheets before being converted by the conversion layer.

Therefore, the combination of Shin and Kurihara renders Claim 1 obvious.

Claim 20 (Display Device with Conversion Layer Between Optical Sheet and Display Panel)

Claim 20 describes a display device including a cover, an LED light-emitting module on the cover, a light guide plate at a side of the module, an optical sheet (diffusion + prism) on the light guide plate, a display panel on the optical sheet, and a conversion layer between the optical sheet and the display panel, converting the light's color after passing through the diffusion and prism sheets.

• Cover & Display Panel: Shin describes a backlight unit for a liquid crystal display (LCD) and explicitly shows a liquid crystal panel (160) on top of the entire backlight unit. [cite: US2007/0147081 A1, Paragraph 0021, FIG. 1] The components would inherently be housed within a cover, a standard feature of display devices. Kurihara also discusses a display device using the phosphor film and lighting device. [cite: US2006/0268537 A1, Abstract, Paragraph 0025]
• Conversion Layer Between Optical Sheet and Display Panel: Shin precisely places the wavelength conversion layer (150) "between the optical sheet (140) and a liquid crystal panel (160)." [cite: US2007/0147081 A1, Abstract, FIG. 1] This layer converts the light's color to a target color, and given its placement, the light from the light guide plate would have passed through any intervening optical sheets.
• Other Elements: The other elements (light-emitting module, light guide plate, optical sheet with diffusion and prism sheets, and color conversion function) are covered by the combination of Shin and Kurihara as discussed for Claim 1.

Thus, Claim 20 is rendered obvious by the combination of Shin and Kurihara.

Claim 23 (Light Source with Reflective Plate and Conversion Sheet Coated on Diffusion Sheet)

Claim 23 describes a light source similar to Claim 1 but specifically adds a reflective plate under the light guide plate and states the conversion sheet is "coated with a color coordinate material on an upper surface of the diffusion sheet" such that it converts the light diffusing by the diffusion sheet.

• Reflective Plate: Shin explicitly includes a reflective sheet (130) positioned "below the light guide plate" (120). [cite: US2007/0147081 A1, Abstract, FIG. 1] The use of a reflective plate to enhance light efficiency is a conventional and obvious practice in backlight units.
• Conversion Sheet Coated on Upper Surface of Diffusion Sheet:
  • The '778 patent itself describes variations in placement, noting that a "color conversion material may be added into the diffusion sheet 141" or "coated with a color conversion material on an upper surface thereof" in its FIG. 3 embodiment. [cite: US8408778B2, Paragraph 0070]
  • While Shin and Kurihara show the conversion layer on top of the entire optical stack (diffusion + prism), the concept of coating a transparent sheet with fluorescent material (Shin [cite: US2007/0147081 A1, Paragraph 0026], Kurihara [cite: US2006/0268537 A1, Paragraph 0036]) was known. A PHOSITA, seeking to optimize the interaction between diffused light and the color conversion material, would find it an obvious design choice to coat the fluorescent material directly onto the diffusion sheet, either as a layer or by integrating it, particularly since the '778 patent explicitly contemplates this arrangement as a variant. Such a placement could optimize light mixing and subsequent direction by prism sheets.

Dependent Claims (e.g., Multi-Rank LEDs)

Dependent claims, such as Claims 8, 9, 24, and 26, relate to the use of LEDs with "different color coordinate distributions within a same color spectrum" or "multi ranks with a wavelength difference within a blue color spectrum."

• Multi-Rank LEDs: Hitachi Displays (US7350937B2) directly addresses this by teaching a lighting unit that uses "a plurality of light emitting diodes (LEDs) of different light emitting colors" or "slightly different wavelengths within the same color (e.g., blue LEDs with peak wavelengths of 450nm and 460nm)" to improve color uniformity and white light. [cite: US7350937B2, Abstract, Paragraphs 0013, 0020]
• Motivation: The motivation to combine the multi-rank LED teaching of Hitachi Displays with the color-converting backlight structures of Shin and Kurihara is to reduce manufacturing costs by allowing for a broader tolerance in LED production (using "multi ranks" or "failure ranks") while still achieving a precise target color output through the conversion layer. This directly aligns with the stated advantages of the '778 patent.

In conclusion, the independent claims (1, 20, 23) and related dependent claims of US8408778 would be considered obvious under 35 U.S.C. § 103 given the combined teachings of Shin, Kurihara, and Hitachi Displays, alongside common knowledge in the field of backlight unit design. The various placements and compositions of the color conversion layer, and the use of multi-rank LEDs, represent predictable design choices and combinations driven by well-known engineering principles and economic motivations in the context of improving LED backlight performance and manufacturing yield.

To detail the information for US patent 8408778, I will refer to the patent text itself and general USPTO guidelines regarding patent term calculations and related applications. The USPTO does not calculate expiration dates for patents; instead, it provides tools and guidelines for estimation.

US Patent 8408778 Details

1. Patent Term Adjustments (PTA)
Patent Term Adjustment (PTA) extends the term of a patent to compensate for delays by the USPTO during prosecution. This patent's Google Patents page indicates an "Adjusted expiration" date of 2031-05-07. This adjusted date implies that PTA was applied to compensate for USPTO delays during the application's prosecution. The specific calculation for PTA (A, B, and C delays, and applicant delays) is typically found in the Issue Notification Letter.

2. Patent Term Extensions (PTE)
Patent Term Extension (PTE) is available under the Hatch-Waxman Act for patents claiming products requiring regulatory approval (e.g., pharmaceuticals, medical devices) to restore patent term lost during the approval process. Given that US patent 8408778 relates to a "Light source and display device," it does not fall under the categories of inventions eligible for PTE. Therefore, it is highly unlikely that any Patent Term Extension was granted for this patent.

3. Continuation Applications
A continuation application allows an applicant to pursue additional claims based on the same disclosure of an earlier "parent" application, maintaining the benefit of the parent's filing date. The patent text for US8408778 (specifically the "Publications" and "Family Applications" sections on Google Patents) does not explicitly list any continuation applications that were filed from US12/698,478 (the application leading to US8408778).

4. Divisional Applications
A divisional application is filed when an invention disclosed in a parent application is deemed to cover more than one independent and distinct invention. Like continuations, they benefit from the filing date of the original application. The provided patent text does not explicitly list any divisional applications that were filed from US12/698,478.

5. Related Family Members
US8408778 is part of a patent family. The provided information shows the following related family members:

• Priority Application: Korean Patent Application No. 10-2009-0013161, filed 2009-02-17. [cite: The provided patent text]
• US Application: US12/698,478, filed 2010-02-02 (which resulted in US8408778B2). [cite: The provided patent text]
• Other Published Applications/Granted Patents within the family:
  • US20100208495A1 (US Publication). [cite: The provided patent text]
  • KR20100093981A (Korean Publication). [cite: The provided patent text]
  • EP2218963A3 (European Publication). [cite: The provided patent text]
  • JP5519317B2 (Japanese Granted Patent). [cite: The provided patent text]
  • CN101806414B (Chinese Granted Patent). [cite: The provided patent text]

6. Projected Expiration Date
The basic term for a U.S. utility patent filed on or after June 8, 1995, is 20 years from the earliest filing date of the application, subject to any Patent Term Adjustments (PTA) or extensions (PTE).

• Earliest Priority Date: 2009-02-17 (Korean Patent Application No. 10-2009-0013161). [cite: The provided patent text]
• US Filing Date: 2010-02-02 (US12/698,478). [cite: The provided patent text]
• Basic 20-year Term from Earliest Filing Date (US Application): 20 years from 2010-02-02 would be 2030-02-02.
• Adjusted Expiration Date: The Google Patents page for US8408778B2 explicitly lists the "Adjusted expiration" as 2031-05-07. This date reflects any PTA awarded due to USPTO delays during prosecution. [cite: The provided patent text]

Therefore, the projected expiration date for US patent 8408778, inclusive of Patent Term Adjustment, is May 7, 2031. [cite: The provided patent text]