Liquid Penetrant Testing Level 2 (PT-2) Practice Exam

The human eye is most sensitive to which of the following types of light?

1. Yellow-green

2. Red

3. Blue-violet

4. Orange

The correct answer is: Blue-violet

The human eye is most sensitive to yellow-green light, particularly around wavelengths of approximately 555 nanometers. This wavelength coincides with the peak sensitivity of the cone cells in the retina, which are primarily responsible for color vision and are most effective in bright light conditions. While blue-violet light is visible to the human eye, it is not the region where the eye's sensitivity peaks. The sensitivity declines for wavelengths on both sides of the yellow-green spectrum, meaning we perceive yellow-green light more easily compared to red, blue-violet, or orange light. This characteristic is especially relevant in applications like Liquid Penetrant Testing, where good visibility of indications is crucial. Understanding this concept is essential not only in visual detection during testing but also in the selection of penetrant colors that provide optimal contrast against various backgrounds. This way, inspectors can achieve accurate and reliable results during testing.