Sensitivity levels are a classification system for fluorescent liquid penetrants which is outlined in AMS 2644 Inspection Material, Penetrant specification. Sensitivity levels are not applied to visible penetrants.
AMS 2644 Sensitivity Levels
Level ½ – Very low sensitivity
Level 1 – Low sensitivity
Level 2 – Medium sensitivity
Level 3 – High sensitivity
Level 4 – Ultrahigh sensitivity
Reasoning for Different Sensitivity Levels
In fluorescent non-destructive testing there needs to be a balance between sensitivity and background fluorescence.