Fluorescent penetrants detect finer crack indications than red, since surface defects under UV light are visible as a bright yellow indicator, which can be seen much better by human eyes in a darkened test.
Furthermore, with the same solution as with a red penetrant, a faster and better evaluation in the series test is possible.

Fluorescent penetrants are divided into 5 possible classes according to DIN / EN / ISO 3452-2 and AMS-2644:

Difference classes:

1/2 insensitive
1 low feeling
2 heard mediocre
3 highly sensitive
4 extremely sensitive