Which statement about how lighting affects defect detectability is true?

• A. Direct lighting creates shadows that reveal edges; oblique lighting emphasizes subtle discontinuities; diffuse lighting reduces glare and provides even illumination.
• B. Oblique lighting hides subtle discontinuities.
• C. Diffuse lighting emphasizes edges.
• D. Lighting has no effect on detection.

Answer: (A)

Lighting direction and quality determine how defects appear by shaping shadows, contrast, and glare on a surface. Direct lighting, coming nearly perpendicular to the surface, tends to cast clearer shadows at edges and along features, boosting edge contrast and making pronounced defects easier to see. Oblique lighting, angled to the surface, shifts shadows across textures and is especially effective at revealing subtle discontinuities like small cracks or texture steps that may be missed under direct light. Diffuse lighting uses scattered light from many directions, reducing glare and providing even illumination, which helps you observe surface uniformity and texture without hot spots that can hide detail. Together, these lighting approaches let you detect different defect types by highlighting edges, subtle irregularities, or overall surface appearance.

So the best statement is the one that says direct lighting creates shadows revealing edges, oblique lighting emphasizes subtle discontinuities, and diffuse lighting reduces glare and provides even illumination. Lighting indeed affects defect detectability, and each lighting condition highlights different aspects of a surface.