Invalidity dossier
US 5921651
Added 9/23/2026, 7:32:27 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 5,921,651 A
Title: Surface light source device of side light type having diffusing element with improved distribution pattern of light
Assignee/Inventor: Original assignee Enplas Corporation; inventor Tsuyoshi Ishikawa (assignment recorded 1996-06-12). Current assignee listed as Enplas Corp.
Key dates (as listed): Priority date 1995-03-31; filing date 1996-03-27; publication/grant date 1999-07-13; anticipated expiration 2016-03-27. Legal status: "Expired – Fee Related" — Google Patents states this is an assumption, not a legal conclusion.
Purpose: The invention addresses side-light-type surface light source devices, useful for backlighting liquid crystal displays. A rod-shaped primary light source (e.g., a cold-cathode tube, called a "lamp") sits along a side edge (incidence surface) of a light guide plate; one plate surface is the luminous surface, with an additional element (diffusing sheet, prism sheet, etc.) and a reflecting sheet opposite it.
The stated problem: when the lamp's emitting portion is shorter than the light guide plate's width, and where non-emitting electrode portions occur at the lamp's ends, luminance can be insufficient near those ends and corners (portion S). Prior patterns—specially treating corner portions F, or radially grading region I versus linearly grading region II about point G—produced sharp density differences or mismatched junctions near such boundaries, causing luminance unevenness or reverse gradients (portions Z).
Plain-language scope (from the excerpt): The claimed approach defines a distribution pattern of light diffusing elements on the rear surface of the light guide plate that (a) excludes any portion where the area-occupation rate of elements decreases from a highly exposable region toward a lowly exposable region, and (b) excludes any portion where that rate varies sharply. The pattern is built in stages, including sizing element "A" so portion B shows no luminance unevenness, and adding a compensating pattern for luminance drop near the non-emitting portion.
What the excerpt does not establish: The full claim text, dependent claims, the complete staged algorithm (numbers/stages are truncated), specific numerical examples, and the precise definitions of regions A/B. The excerpt is explicitly partial ("[Excerpt only; consult the source for omitted text.]").
Generated 10/1/2026, 9:41:58 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.