Optical methods

What is NDT? 

Optical methods were probably the first techniques to be used for non-destructive testing, notably visual testing. They have developed from ancient origins into many complex and elaborate optical investigation techniques. Some visual tests are based on the simple laws of geometrical optics. Others depend on properties of light, such as its wave nature. A unique advantage of many optical methods is that they can yield quantitative results more readily than other non-destructive tests.