Persistence of Bacteria in UV-C Shadow Regions
UV-C sterilization is admissible as complete only if microbial inactivation is independent of geometry. If viable organisms persist in shadowed regions under standard exposure, sterility becomes line-of-sight constrained rather than exposure-defined.
UV sterilization does not fail by dose—it fails by geometry. If light cannot reach a surface, sterility cannot be assumed.
Exposure implies sterility
The assumption is that UV-C exposure at validated intensity and time ensures complete inactivation of surface bacteria regardless of object geometry.
Sterility is line-of-sight constrained
UV-C radiation propagates directionally and does not penetrate opaque materials or reach geometrically shadowed regions.
This creates protected survival zones where organisms remain viable despite compliant exposure conditions.
Geometric visibility to radiation
The governing variable is not dose, but whether each surface region has direct line-of-sight exposure to the UV source.
- Visible surface → high inactivation probability
- Shadowed surface → survival-protected region
Shadow vs exposed comparison
- Defined shadow geometries using matte objects
- Controlled UV-C exposure (254 nm, fixed intensity/time)
- Identical inoculation across exposed and shadowed regions
- CFU recovery and quantification
Only geometry differs. All other variables are held constant.
What breaks the assumption
Pass: Zero CFU across all regions regardless of geometry.
Fail: ≥1 CFU detected in any shadowed region.
Sterility requires coverage, not exposure
Sterilization cannot be defined solely by time and intensity. It requires complete geometric coverage of all surfaces.
Exposure metrics without spatial completeness are insufficient to guarantee sterility.
A surface cannot be sterilized if it cannot be seen.
Sterility is not a function of exposure alone. It is a function of exposure plus visibility. Geometry defines the true boundary.
Status: Final · Immutable