Lighting

Lighting is one of the most critical components of a vision solution. The selection of the appropriate lighting component for an application is critical to ensure the vision system performs its tasks consistently and reliably. 

The role of application-specific lighting is to ensure that all features of interest are isolated and visible contrast is created between the object and background. In most cases, software cannot “fix” or create visible contrast if a feature is not correctly illuminated.

Keep the "Big Picture" in Mind

Choosing the right lighting is just one part of setting up your image capture system. Make sure you also select the right camera and lens.

The guiding principle in developing your camera, lens, and lighting system is that it should lead to reliable and repeatable results. Good data in leads to good data out.

Goals of Lighting Systems

The goal of a lighting system in a computer vision application is to:

• Maximize the contrast of the features to be inspected or measured
• Minimize the contrast of the features of no interest
• Remove unwanted variations caused by ambient light and unwanted differences that are not relevant to the inspection task.

It may be necessary to perform feasibility studies with different lighting options to isolate features of interest. 

Lighting Best Practices

Our partner, Smart Vision Lights, provides the “A-T-E-S-T” method to help users identify the effects of different lighting techniques on part features:

Lighting Best Practices from Our Partner, Smart Vision Lights

Key Lighting Parameters

To choose the most suitable light for a project, consider the following parameters:

• Lighting geometry, which is the arrangement and interaction between light sources and objects.
• Light source type
• Wavelength
• Surface characteristics of the material to be inspected, such as color and reflectivity
• Object shape
• Item speed
• Mechanical constraints
• Cost

LED Light Pulsing and Strobing

LED lights can be used continuously to illuminate an object. Alternatively, LED’s can be pulsed (on or off) turning them on when necessary.

An LED is in pulsed mode if the LED driving current or voltage is set to the nominal value declared by the LED manufacturer for a specific amount of time and reset to zero. Pulsing offers the following advantages:

• Preserves the lifespan of the light
• Reduces power dissipation
• Reduces heat generation

An LED is in strobed mode if the LED is driven at higher intensity than the nominal value (over driven) producing more light for a nominal amount of time. Strobing offers the following advantages:

• Ideal when the application requires an increased amount of light to “freeze” the motion of the object 
• Eliminates the effects of ambient light
• Preserves the lifespan of the light

Can I use ambient light?

It might be tempting to use ambient light—in other words, whatever light is available—to get images. However, the specific type of lighting, or changes in lighting, can have a big impact on objects or defects showing up consistently in photos. 

For example, if you want to detect fine cracks on a metal surface, then the lighting in your production floor might create shadows or reflections on metal objects, hindering the camera's ability to take an accurate image. 

We generally recommend implementing a lighting solution that is controlled and ensures consistent results.