Lighting is one of the most critical aspects of machine vision applications. Failure to properly illuminate a target can result in the loss of information and productivity. A lighting technique involves a light source and its placement with respect to the part and the camera. Cognex vision systems offer various combinations of external and integrated lighting options based on the environment and application.

Back Lighting

Back lighting projects even illumination from behind the target highlighting the silhouette of the target. This lighting type is used to detect the presence/absence of holes or gaps, measurement or verification of the target outline shape, as well as enhancing cracks, bubbles, and scratches on clear target parts. Note that surface detail is lost with this lighting type.

Bar Lighting

Bar lighting provides a strip of light on the target or along the edge of the target for uniform illumination along the localized area. It can be combined with other bar lights to cover the entire target from all directions. Depending on the angle of the light and camera, bar lighting can enhance or reduce specular reflection. It's used to add contrast to matte surfaces such as paper or cardboard, define edges, or highlight surface features.

Dark Field Lighting

Dark field lighting technique provides a light at a shallow angle to the target. Any surface features–scratches, edges, imprints, notches–reflect the light back to the camera making these surface features appear bright, while the rest of the surface is dark. This technique can be created with any directional lighting option (bar, ring, spot) that allows for the light to be angled to the part's surface.

Diffuse On-Axis (Co-axial) Lighting

Diffuse on-axis lighting, also referred to as co-axial lighting, transmits lighting perpendicular to the target and uses a mirror to send the light rays at a 90-degree angle to the target. This technique will highlight specular surfaces perpendicular to the camera. Surfaces that are at an angle to the camera will be dark. This lighting technique reduces shadowing and has very little glare. This makes it useful to detect flaws on shiny, flat surfaces, measurements or inspection on shiny objects, or to inspect transparent packaging.

Diffuse Dome/Ring Lighting

Diffuse lighting technique scatters light to reduce glare on reflective parts. This technique can be applied to all directional lighting (bar, dome, ring) to provide a more uniform spread of light across the target. This lighting technique is helpful in reducing lighting noise like glare and hotspots from on-axis directional lights such as ring lights.

Dome Lighting

Dome lighting provides uniform light from various angles which results in no glare, even on mirrored objects. It's often referred to as "cloudy day" illumination since it removes uneven lighting (glare/shadows) and evenly spreads the lighting across the surface of the part. Dome illumination is used most often to inspect shiny, curved, or bumpy surfaces. To be effective, dome lights require close proximity to the target.

Low Angle Dark Field Lighting

Low angle dark field lighting technique provides a light at an extremely shallow angle (10-15 degrees) to the target. Any surface features including dust, scuffs, and even finger prints on a mirrored surface reflect the light back to the camera making these surface features appear bright, while the rest of the surface is dark. This lighting technique is especially good to use for surface inspection on shiny, highly reflective targets. Any height differences on the surface are highlighted.

Ring Lighting

Ring lighting is a circle or ring of bright, intense lighting that provides shadow-free illumination and good image contrast. Ring lighting is a common lighting type covering a broad range of applications due to its versatility. Note that it can cause specular glare on reflective parts.

High-Powered Integrated Light

High-powered integrated light (HPIL) provides direct polarized or non-polarized light onto the target. HPIL is available for select In-Sight 7000 vision systems.

In-Sight Integrated Light

The In-Sight integrated light is a diffuse ring light that provides bright uniform lighting on the target for machine vision applications. This integrated light reduces shadowing and provides uniform illumination on matte objects. Due to the diffuse nature of the light, at closer working distances (less than 70mm), the light also provides a dark field lighting technique. The In-Sight Integrated Light is available for select In-Sight 7000 vision systems.

Color Filters

Color filters create contrast to lighten or darken features of the object. Like color filters lighten (i.e. red light makes red features brighter) and opposite color filters darken (i.e. red light makes green features darker).


Polarizers are filters placed in front of the camera lens and LEDs at a 90-degree offset. Polarizers are used in imaging applications to reduce glare or hot spots and enhance contrast so entire objects can be recognized.

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