How do fluorescent penetrants differ from visible dye penetrants?

Fluorescent penetrants are specifically formulated to be visible only under ultraviolet (UV) light, making them undetectable under normal ambient lighting conditions. This characteristic allows for enhanced sensitivity and the ability to reveal defects that may not be visible with standard visible dye penetrants. When a component is inspected using fluorescent penetrants, the presence of a defect is indicated by a bright fluorescent glow under UV light, which provides a clear contrast against the background, making it easier to identify potential issues.

In contrast, visible dye penetrants can be seen with the naked eye under normal light conditions, which may not always be ideal in cases where surface reflections or lighting conditions could obscure the visibility of a defect. Therefore, option B accurately highlights the key distinction between the two types of penetrants regarding their visibility under standard lighting versus UV exposure.