absence of surface contamination when examined with a specific light source, angle of incidence and viewing distance using normal or magnified vision
NOTE 1 Different inspection methods are available, depending on:
a. hardware to be inspected, in term of size and accessibility and sensitivity to contamination
b. inspection distance
c. light spectra (including UV), intensities and angles
NOTE 2 The 'visibly clean' level roughly corresponds to an obscuration factor smaller than 300 mm2/m2 when inspected from a distance of 30 cm to 60 cm with an oblique white light of 540 lx to 1620 lx.
NOTE 3 Typical magnification levels range from 2x to 8x.