Need for clarity in military standards pertaining to levels of optical radiation in penetrant and magnetic particle NDT inspection processes

Unfortunately, most photometers are badly matched to the challenge of measuring low levels of any color visible light and even more so for low-level blue/violet light. This is because of the eye's spectral response shift and increased sensitivity at low light levels and also because light meters in general do not have correct blue/violet response, even at high levels. However, for the Type II nonfluorescent penetrants and magnetic particles, conventional «general-purpose» light meters are sufficient at present, provided that they have adequate illuminance range, MIL-STD-6866 and MIL-STD-1949 currently requiring a minimum of 200 ftc (2150 lx) and 100 ftc (1070 lx), respectively, for visible dye inspection and nonfluorescent magnetic particle methods