For manual inspection of the glasses, the light is usually shed in top-down way. A white plate is placed beneath the glass sheet. The inspector checks the glasses and marks observable defects with a chuck.
This type of inspection is carried out by a laser scanner, image processing and signal transfer throughout the glass width. The inspection takes place for the defects in the glass in formation parts and for defects such as bulb, sand, stone, sticking tin to the glass, light refraction, etc.
ADG-90 automatic inspection system designed in China can inspect defects with minimum dimension of 0.2 mm×0.2 mm. The inspection reliability reaches to 100% for the defects larger than 0.5 mm and such reliability is 90% for the sizes 0.3-0.5 mm.