Invalidity dossier
US 5797668
Added 9/23/2026, 9:17:37 PM
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Patent summary
Title, assignee, inventors, filing/issue dates, abstract, and a plain-language overview of the claims.
Patent Overview — US 5,797,668 A
Title: Surface illumination device suitable for a backlit display
Patent number: US5797668A
Application number: US08/832,047
Filing date: 1997-04-02
Priority date: 1996-04-04
Publication (grant) date: 1998-08-25
Inventors: Hiroshi Kojima; Nobuo Naito
Original/current assignee (as listed): Dai Nippon Printing Co., Ltd.
Legal status (as listed): Expired – Lifetime; anticipated expiration 2017-04-02
Classifications (selected): G02B6/00, G02B6/0011, G02B6/0033, G02B6/005, G02B6/0053, G02B6/0046
Purpose and plain-language scope. The patent concerns an edge-lit "surface illuminant" (backlight) for a transmissive liquid crystal display, advertisement board, and similar uses, aimed at using light efficiently. A conventional arrangement comprises a lens film, a light guide plate behind it, a light source along a side edge, a diffusing film between them, and a reflecting member behind the guide plate, with printed white dots whose density increases with distance from the light source to even out emitted light.
The described device pairs a light guide plate, which emits light through an exit surface, with a lens film facing that surface. The lens film has triangular prisms of isosceles-triangle cross-section on its exit side. The two are related so that the peak exit angle θ1 of light from the guide plate, the prism apex angle θ2, and the lens film refractive index n satisfy the relationships recited in the patent (0.5 ≤ R ≤ 1.0, with R defined by the stated equation). So designed, most light leaving the guide plate at the peak angle exits the lens film substantially parallel to the normal of its imaginary exit surface, making the device appear brightest when viewed head-on.
What the excerpt does not establish. It does not provide the full claim set, the equation as rendered (the text shows ##EQU2##/##EQU3## placeholders), the complete description, drawings, or prosecution history. It establishes no litigation, ownership transfer, validity, or prior-art conclusions. Source: https://patents.google.com/patent/US5797668/en
Generated 10/1/2026, 9:34:24 PM
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Litigation summary
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Proceedings on file (0)
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No PTAB proceedings on file. This patent has not been challenged via IPR, PGR, or CBM. The absence is itself a signal — well-asserted patents eventually attract IPRs. The LLM analysis below may surface filings the ODP feed hasn’t indexed yet.
PTAB challenges
AIA trial proceedings at the USPTO Patent Trial and Appeal Board — IPR, PGR, and CBM. Petitioners, judge panels, claim-level invalidation outcomes from Final Written Decisions, and Federal Circuit appeals. The single most important defensive datapoint after litigation history.
Assignment history
Inventors, original assignee, and the chain of ownership recorded with the USPTO — including the correspondent attorney who recorded each assignment, since shell-LLC chains often share one repeat-player attorney even when the entity names look unrelated. Surfaces NPE / patent-troll patterns: shell-entity transfers, known asserters in the chain, repeat correspondent fingerprints, pre-litigation assignments, and bankruptcy fire-sales.
Prior art
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Obviousness
Combinations of prior art that suggest the claimed invention would have been obvious under 35 U.S.C. § 103.
Extensions
Patent term adjustments, term extensions, continuations, divisionals, family members, and expiration dates.
Derivative works
Defensive disclosure: derivative variations of each claim designed to render future incremental improvements obvious or non-novel.