Many of the defects found in PET container preforms can be detected by using the PL-P. Preforms viewed in polarized light exhibit a colored birefringence pattern.

The birefringence is a result of the polymer flow lines (molecular orientational strain) produced during the injection moulding process.

The colored pattern observed with preform held at 45° to the polarizing axis is known as an isochromatic fringe indicating the amount of birefringence.

When the preform is held parallel to the polarizing axis a black isoclinic can be seen indicating the direction of the molecular orientational strain.By correctly interpreting these flow patterns many preform defects can be detected.

With angle adjusting design, operator can view the preform as their most convenience angle. And the upgraded wider viewing area and sample platform, more preforms could be placed and viewed in the same time. It also frees the hands of operator.