Basics of Lighting Selection

(1)Sample image of specular reflection

Inspecting for the presence or absence of inscriptions on metal surfaces

1. The inscription is unclear.
2. The inscription is clear.

It is necessary to bring out the contrast between the flat metal surface and depressions of the inscription

Since a metal surface reflects light easily and the inscription does not, the optimum method is to use specular reflection to enhance the difference between the surface and inscription.

(2)Sample image of diffuse reflection

Inspecting the print on a chip through transparent film

1. The Lighting reflects on the film surface.
2. The image is not affected by the film.

It is necessary to bring out the contrast between the surface of the chip and the print by eliminating the reflection from the transparent film (halation).

The optimum method is to use diffuse reflection to prevent specular reflection on the transparent tape.

(3)Sample image of transmitted light

Inspecting foreign matter on nonwoven fabric

1. The Lighting reflects on the film surface.
2. The silhouette of the foreign matter is clearly recognized.

It is necessary to bring out the contrast between the target surface and the foreign matter, which is difficult to recognize because of the subtle difference in color.

Even when no difference can be detected with reflected light, applying transmitted light from behind the target will show foreign matter as a black silhouette.

(1)Sample image of specular lighting
Detecting chips in the edge of a glass plate

Simple reflected light

Reflected light is reflected randomly on the glass surface.　

【Selecting lighting according to the work piece characteristics and detection details】

• The light reflects on the glass surface.
• It is necessary to enhance the difference between the glass plate and background.
• It is best to apply lighting vertically to the work piece.
• A space can be provided above the work piece.

The best selection is coaxial-vertical lighting.

coaxial-vertical illumination
The entire glass surface can be illuminated uniformly.

(2)Detection example of diffuse reflection
Inspecting chips in rubber packing

Simple reflected light

The chips on the outer-circumference cannot be recognized.

【Selecting lighting according to the work piece characteristics and detection details】

• The work piece is black rubber which does not reflect specular light.
• The chipping is also black and will not reflect specular light.
• Illuminating the work piece from an angle to reflect the specular light from the chipped area proves effective.
• A light can be installed close to the target.

The best selection is low-angle light.

(3)Detection example of transmitted light
Inspecting lead shapes

Simple reflected light

The edges show little contrast.

【Selecting lighting according to the work piece characteristics and detection details】

• The target is a metal object with projections and depressions, resulting in irregular specular reflection.
• By using a transmitted light, the edge of the target can be detected without the influence of the projections and depressions.
• A light can be installed behind the work piece.

The best selection is a backlight.

With a backlight
The complicated outline can be recognized clearly.