Machine Vision Lights: Choose the right illumination for your machine vision system

Lighting plays a critical role in the performance of a machine vision system, especially for tasks like defect detection, measurement, inspection, counting, and tracking. Proper lighting enhances image quality, ensuring accurate processing and reliable results. The right combination of lighting techniques and angles can make the difference between success and failure in defect detection.

Types of Lighting in Machine Vision

Backlighting:

Backlighting illuminates the object from behind, creating a sharp contrast between the object and the background. It is ideal for edge detection, measurement, and silhouette-based inspections.

Common applications: Gauging, profile inspection, and detection of transparent materials.

Diffuse Dome Lighting:

This lighting provides even, shadow-free illumination by reflecting light from a dome-shaped surface. It is perfect for highlighting subtle surface features without causing glare.

Common applications: Inspection of shiny or reflective surfaces like metal, glass, or plastics.

Ring Lighting:

Positioned around the camera lens, ring lights provide uniform, directional light toward the object. This method is useful for general-purpose lighting and can help to reduce shadows.

Common applications: Inspection, tracking, and counting of small objects.

Dark Field Lighting:

This technique involves placing the light at a low angle, which highlights surface textures, scratches, or defects by casting shadows on the surface imperfections.

Common applications: Surface defect detection in materials like glass, plastic, and polished metals.

Coaxial Lighting:

Coaxial lighting is a type of illumination that emits light vertically onto a target from the same axis as the camera and lens. It's also known as brightfield illumination or diffuse on-axis lighting

Common applications: Inspection of flat, reflective surfaces such as wafers and LCD panels.

Structured Lighting:

Projecting patterns like grids or stripes onto an object, structured lighting can enhance 3D surface inspection and measurement.

Common applications: Height measurement, 3D inspection, and volume analysis.

Choosing the right Illumination for your Machine Vision Systems

Selecting the ideal lighting for a machine vision system requires careful consideration of various factors, each influenced by the object being inspected, the features that need to be detected, and the layout of the system. To ensure precise illumination, ask yourself the following:

Field of view and object size: How big is the area you need to capture, and what are the dimensions of the object?

Distance to camera and lighting: How far is the object from both the camera and the light source?

Type and intensity of light: What lighting method and brightness level will provide the best illumination for accurate inspection

Feature characteristics: What are the specific attributes of the features you’re inspecting, and which lighting technique will best reveal them?

Surface properties and material: What is the texture and material of the object, and how will these affect the way light interacts with it?

Object color: Does the object’s color call for a particular light color to enhance contrast? Consider options such as white, red, blue, green, or specialized lighting like infrared (IR) or ultraviolet (UV).

Types of Illumination in Machine Vision

In machine vision, several types of lighting sources are commonly used:

Fluorescent: Popular for small- to medium-scale inspection stations due to its efficiency and widespread availability.
Quartz Halogen: Known for its greater intensity, making it suitable for inspections that require strong illumination.
LED: Offers long life expectancy and is highly adaptable, making it a common choice for many inspection stations.
Metal Halide (Mercury): Frequently used in microscopy due to its discrete wavelength peaks, ideal for fluorescence studies.
Xenon: A powerful source for applications that require a bright strobe light, often used in large-scale setups.

Each lighting type serves different purposes depending on the scale of the inspection and the specific lighting requirements.

Lighting Angle and Reflection Management

The angle at which light hits the object is crucial in machine vision systems. Improper lighting angles can result in reflection or glare, which can obscure details and lead to inaccurate analysis.

Low-angle lighting: Enhances surface textures and highlights defects by casting long shadows.
High-angle lighting: Minimizes shadows and reflection but may reduce the visibility of fine surface details.
Adjusting the angle: By carefully adjusting the lighting angle, you can avoid unwanted reflections and achieve optimal contrast, ensuring that even the smallest defects are detected.

The Role of Diffusers in Machine Vision

What is a Diffuser?

A diffuser is a translucent material used to scatter light, providing soft and even illumination across the object. It helps eliminate shadows and hotspots, which can otherwise interfere with the machine vision system's accuracy.

Why and How it is Used

In machine vision, diffusers are essential when inspecting highly reflective surfaces. Without a diffuser, light reflections can create bright spots or glare, causing the camera to miss important details. A diffuser helps by spreading the light more evenly, reducing the harsh reflections and allowing the system to capture clearer, more uniform images.