What distinguishes fluorescent penetrant dyes from visible ones?

Fluorescent penetrant dyes are distinguished from visible ones primarily by their ability to fluoresce under ultraviolet (UV) light, which results in a striking color intensity in the dark. When exposed to UV light, the fluorescent penetrant dye emits a bright, vivid color that allows for better detection of flaws and discontinuities on the surface of materials, especially in welds and other critical components. This property greatly enhances visibility and sensitivity, making it easier for inspectors to identify defects that may not be as easily seen with visible dyes, which do not possess this fluorescence capability.

The other aspects such as viscosity, cost, and application methods may vary between different types of penetrant dyes, but the fundamental characteristic that sets fluorescent dyes apart is their fluorescent response under UV light, making them particularly effective in non-destructive testing applications.