What indication will be seen when fluorescent penetrant is exposed to black light?

When fluorescent penetrant is exposed to black light, it fluoresces brightly, resulting in bright fluorescent indications. This happens because the penetrant contains specific dyes that are designed to absorb ultraviolet (UV) light and then re-emit it in the visible spectrum, typically appearing as a bright green or yellow glow. This bright fluorescence makes it easier to identify surface defects in the material being inspected, such as cracks or porosity, which are critical for ensuring the integrity of components in various applications, particularly in aerospace and manufacturing.

The other options reflect potential misunderstandings of the properties of fluorescent penetrants under UV light. For example, stating that there are no indications at all would misrepresent the purpose of using fluorescent methods, as they are specifically intended to reveal defects. Dim fluorescent indications do not align with the pronounced brightness that is a hallmark of properly formulated fluorescent penetrants when illuminated by a black light. Similarly, color changes without fluorescence would not apply in the context of fluorescent penetrants since their primary function is to fluoresce under UV light.