Liquid Penetrant Testing Level 1 (PT-1) Practice Exam

What is the most desirable center wavelength for the output of the light source in fluorescent process?

1. 3000 A (300 nm)

2. 3650 A (365 nm)

3. 4500 A (450 nm)

4. 5000 A (500 nm)

The correct answer is: 3650 A (365 nm)

In the fluorescent liquid penetrant testing process, the most desirable center wavelength for the light source output is indeed 3650 Å (365 nm). This wavelength falls within the ultraviolet (UV) spectrum, which is optimal for exciting the fluorescent penetrants typically used in these tests. Fluorescent penetrants are designed to absorb UV light at this specific wavelength and re-emit it at a longer wavelength that is visible to the human eye. Using a light source that emits at 365 nm ensures maximum excitation of the fluorescent particles in the penetrant, leading to a brighter and more easily detectable indication of any flaws present on the surface of the material being tested. Light sources at wavelengths much lower than 365 nm (such as 300 nm) may not yield the desirable results since they can be less effective at exciting the particular types of fluorescent penetrants used, and ultraviolet light in the range of 450 nm to 500 nm falls outside the optimal excitation range for these materials, resulting in poorer visibility of any indications. Therefore, a light source emitting at 365 nm is crucial for achieving the best performance in fluorescent penetrant testing.