Choose the right machine vision lighting: Ring and bar lights

When it comes to machine vision applications, the lighting you choose makes all the difference.

Among the many lighting options available, ring lights and bar lights have earned their place as the most popular choices. Their design and functionality make them ideal for everything from simple imaging tasks to more complex setups requiring fine-tuned adjustments. Let’s explore why these two form factors are the go-to solutions for so many applications.

The basics of ring lights and bar lights

When choosing the right lighting for machine vision, ring and bar lights each offer unique advantages suited to different applications. Below, we’ll explore their key benefits and considerations.

Ring lights

As the name suggests, ring lights form a circular pattern of light around the camera lens. This design ensures even illumination of the target area and is especially effective for brightfield imaging.

Key benefits of ring lights:

• Simplicity: Mount directly to the camera or its support structure for a one-stop solution, making setup quick and straightforward.
• Uniform illumination: Ideal for capturing detailed images without harsh shadows or uneven lighting.
• Compact design: Perfect for tight spaces to reduce the space required, or to centralize the vision system around the camera.

Ring lights are particularly well-suited for applications requiring uniform illumination around an object, especially when the light source needs to be close to the camera and aligned with its optical axis.

Ring light considerations:

• Limited adjustability: Not ideal for situations requiring flexible angles or working distances.
• Field of view constraints: The light’s diameter must match or exceed the camera’s field of view, which can limit use with larger objects.

Bar lights

Bar lights, or linear lights, are elongated light sources that provide flexible and adjustable lighting for a variety of applications. Typically used in pairs or sets, they offer unmatched control for large or irregularly shaped objects.

Key benefits of bar lights:

• Highly adjustable: Control height, angle, and distance to achieve precise illumination.
• Versatile configurations: Use one, two, or four bar lights to ensure even coverage across larger areas.
• Adaptable to constraints: Ideal for side-mounted setups or scenarios where overhead space is limited.
• Greater light output: A pair of bar lights often provides more total light than a comparable ring light solution.

Bar lights excel in applications that demand broader, customizable light coverage, making them ideal for large objects or setups with complex geometries.

Bar light considerations:

• Setup complexity: Requires precise mounting and alignment, which can increase setup time.
• Maintenance: Vulnerable to misalignment, especially in dynamic environments.
• Cost: Because they are often used in pairs, bar lights can increase the overall investment.

Comparing ring and bar lights to other options

While spotlights, dome lights, and backlights have their place in machine vision, they often fall short in versatility and adaptability compared to ring and bar lights.

• Spotlights: Offer intense illumination but can create shadows and glare, limiting their effectiveness for uniform imaging.
• Dome lights: Provide diffuse light but lack adjustability and are impractical for detailed imaging.
• Backlights: Great for silhouette imaging but not suited for applications requiring surface inspection.

In contrast, ring and bar lights excel in scenarios requiring controlled lighting, flexible setups, and precise adjustments to optimize image quality.

Bar lights and ring lights: Practical machine vision lighting examples

When selecting between ring and bar lights, the decision often depends on the object being inspected and the lighting challenges presented by its geometry, texture, and reflectivity. The following examples illustrate how these considerations play out in real-world applications.

Example 1: Cooling fan inspection

This example involves a small cooling fan with a shiny metallic label and black plastic housing—a challenging combination due to its reflective surface and textured materials.

Bar light setup

Bar lights are positioned on either side of the fan, angled to create uniform lighting while minimizing glare on the shiny label. This setup is ideal if glare or uneven illumination becomes a problem, as the adjustability of bar lights allows precise control over the angle and distance to correct these issues.

Ring light setup

A ring light is mounted around the camera lens to provide uniform illumination directly over the fan. This simpler setup works effectively if there are no significant glare issues, offering a cost-effective and easy-to-implement solution.

Key takeaway

For straightforward imaging tasks, a ring light is often sufficient and more affordable. However, if glare or other challenges arise, the adjustability of bar lights can provide the necessary flexibility.

Example 2: Gear inspection

The second example focuses on a gear with angled splines, a highly specular surface that requires careful lighting to capture details effectively.

Bar light setup

Bar lights are positioned in pairs to achieve a dark field effect. However, due to the gear’s angled splines, reflections disrupt the uniformity of the image. Achieving optimal lighting would require four bar lights placed around the gear to balance the reflections and create a consistent dark field image—a complex and resource-intensive setup.

Ring light setup

A dark field ring light positioned at the appropriate distance provides effective dark field illumination with minimal effort. Its circular design evenly distributes light across the gear, capturing the surface details without requiring additional adjustments.

Key takeaway

The gear’s unique geometry and reflective surface highlight how the object dictates the lighting choice. While bar lights offer exceptional flexibility and can work with sufficient adjustments, the ring light proves to be the more practical option in this case due to its simplicity and effectiveness at achieving the desired dark field effect. This example underscores the importance of matching the lighting method to the specific requirements of the object being inspected.

Watch the video: Select Machine Vision Lighting Like a Pro

Whether you’re inspecting tiny components or large objects, ring and bar lights deliver:

• Precision: Control over lighting angles, distance, and intensity.
• Flexibility: Adaptability to different object sizes and imaging challenges.
• Consistency: Reliable, repeatable results in demanding machine vision applications.

When your goal is to achieve the highest-quality images with the least hassle, ring and bar lights are the clear choice.