Provided is a method and an apparatus for indicating minimum exposure of a surface to UVC light emitted by a source during a decontamination process to achieve a desired level of pathogen reduction. The apparatus includes a photochromic material to be applied to, or applied adjacent to the surface. The photochromic material is to exhibit a visible response to receiving the minimum exposure to the UVC light, and exhibit the visible response to a lesser extent after the photochromic material ceases to be exposed to the UVC light emitted by the source. A protective layer of material that is substantially transparent to the UVC light emitted by the source is positioned over the photochromic material to be disposed between the source and the photochromic material during the decontamination process.
