Conciseness

The body is mostly lean, prop-annotated code, but it explains basic three.js concepts Claude already knows ("Illuminates all objects equally. No direction, no shadows.", "Emits light in all directions. Like a light bulb.") and repeats import/boilerplate across many snippets. It could be tightened, matching the 'mostly efficient but includes some unnecessary explanation' anchor rather than the fully lean anchor 4.

Actionability

Nearly all guidance is concrete, executable TSX covering the common cases (Quick Start, every light type, Environment, Stage, ContactShadows), but there are minor gaps: component snippets omit React imports, and "useHelper(lightRef.current?.shadow.camera, CameraHelper)" passes a resolved value where a ref is required. This fits 'mostly executable guidance with minor gaps' rather than the fully copy-paste-ready anchor 5.

Workflow Clarity

Sections are clearly organized (overview table, per-type reference, complete ready-made setups like Three-Point Lighting and Studio Lighting) and no destructive/batch operations require validation. However, there is no guidance for choosing among the overlapping shadow/lighting approaches (e.g., ContactShadows vs AccumulativeShadows vs shadow maps), leaving the apply-which-one workflow implicit, so it stops short of anchor 5.

Progressive Disclosure

All ~670 lines live inline in SKILL.md with zero bundle files or reference pointers — the per-light prop reference, the entire drei helpers catalog (Environment, Lightformer, Sky, Stars, Stage, ContactShadows, AccumulativeShadows, SoftShadows, BakeShadows), common setups, and animation patterns are content that clearly belongs in separate reference files. In-file section headers are better than anchor 2's 'no section headers' example, but the complete absence of any cross-file disclosure for a 670-line reference puts it noticeably below the midpoint between anchors 2 and 3.

Specificity

It names the domain ("React Three Fiber lighting") plus concrete topics ("light types, shadows, Environment component, IBL") and multiple concrete actions ("adding lights, configuring shadows, setting up environment lighting, or optimizing lighting performance") that comprehensively span the lighting domain, matching the multiple-specific-actions anchor. It is not anchor 4 because the enumerated actions leave no significant coverage gap for this domain.

Completeness

It explicitly answers both what ("light types, shadows, Environment component, IBL") and when ("Use when adding lights, configuring shadows, setting up environment lighting, or optimizing lighting performance") with concrete trigger phrases, exactly matching the anchor 5 example pattern. Not anchor 4, since the 'when' clause is fully explicit with multiple concrete triggers.

Trigger Term Quality

Natural phrases users would actually say are present ("adding lights", "configuring shadows", "environment lighting", "lighting performance"), giving good keyword coverage. It falls short of anchor 5's comprehensive synonym coverage: common variations like "HDR/HDRI", "light setup", or "illumination" are missing.

Distinctiveness Conflict Risk

"React Three Fiber lighting" carves out a clear niche with distinct triggers; adjacent skills (r3f-materials, r3f-textures, r3f-postprocessing) cover different concerns, and only minimal overlap exists (e.g., bloom effects). It matches the clear-niche/minimal-conflict anchor rather than the minor-overlap anchor 4.