In the earlier parts of our series, we examined lighting types and the correct light configurations based on surface characteristics. However, achieving a flawless image in industrial machine vision doesn't end with merely shining light onto the object from the right angle. Many deep parameters come into play, from the color of the light (wavelength) and its parallelism (collimation) to its polarization and optical filters. Let's begin exploring the world of Advanced Lighting Parameters and Optical Interactions, where we aim to eliminate ambient noise and highlight hidden defects by controlling the behavior of light down to the photon level.
2.4 Advanced Lighting Parameters and Optical Interactions In industrial machine vision systems, lighting is not limited to simply selecting a light source. The physical properties of light, its interaction with the object, and optical control methods are advanced design parameters that directly affect image quality. In this section, we delve into the deeper optical characteristics of lighting.
2.4.1 Light-Object Interaction The interaction between light and an object occurs through four fundamental mechanisms:
Reflection
Scattering
Absorption
Transmission
These interactions vary depending on the physical properties of the surface:
Glossy/Shiny surface → Specular reflection
Matte surface → Diffuse scattering
Transparent surface → Light transmission
Proper lighting design is achieved by controlling these interactions. For instance, scattering is increased to make surface defects visible, while reflection is controlled to reduce glare.
2.4.2 Wavelength and Imaging Techniques The wavelength (color) of light is a crucial parameter that directly impacts imaging performance.
Color: Different wavelengths create different contrasts on the object's surface.
Red light → Deep penetration
Blue light → Highlights surface details
Green light → Provides an overall balance
Scattering, Diffusion, Transmission:
Diffuse light → Homogeneous image
Directional light → Reveals surface defects
Backlight → Used for geometric analysis
Fluorescence: Some materials absorb light at a specific wavelength and emit light at a different wavelength. This technique is particularly used in:
Coating inspection
Chemical analysis
Defect detection under UV light applications
2.4.3 Degree of Collimation Collimation refers to the degree of parallelism of light rays.
High collimation (parallel light):
Sharp edge detection
Measurement applications
Low collimation (diffused light):
Homogeneous illumination
Glare reduction
Collimated light is of critical importance, especially in telecentric systems and precision measurement applications.
2.4.4 Polarization Polarized light consists of light waves vibrating in a specific plane. Polarization techniques are used for:
Reflection control
Glare reduction
Transparent surface analysis
It is particularly used to eliminate unwanted reflections on:
Glass
Plastic
Shiny metal surfaces
2.4.5 Light Intensity Light intensity determines the image brightness and signal quality.
Low light → Increased noise
High light → Risk of saturation
Light intensity must be optimized in conjunction with the following parameters:
Exposure time
Aperture (f-number)
Camera sensitivity
2.4.6 Optical Lighting Components (Filters and Diffusers) Optical components used in lighting systems are intended to control the spectral and geometric properties of light. These elements play a critical role in increasing image contrast, eliminating unwanted light components, and obtaining a more stable image.
2.4.6.1 Filters Filters optimize image quality by selectively transmitting specific wavelengths. They are widely used in industrial machine vision systems, especially for contrast enhancement and noise reduction.
Band-pass filters only transmit light within a specific wavelength range and block all other wavelengths.
High contrast is achieved
The effect of ambient light is reduced
Particularly used in synchronized operations with LEDs
These filters are preferred in imaging applications conducted within a specific color or spectral range.
Long-pass filters transmit light above a certain threshold wavelength while blocking shorter wavelengths.
Used in IR (infrared) imaging applications
Reduces the effect of ambient light
Widely preferred in fluorescence applications
They are highly effective especially in situations where visible light needs to be suppressed to analyze specific spectral components.
Polarizing filters only allow light vibrating in a specific plane to pass through.
Glare is reduced
Reflection is controlled
Image quality is improved on transparent and shiny surfaces
Maximum effect is generally achieved by using cross-polarization (light source polarizer + lens filter).
2.4.6.2 Diffusers Diffusers provide more homogeneous illumination by scattering the light.
Soften harsh shadows
Minimize glare problems
Create an even distribution of light across the surface
They are critically important especially for:
Shiny/glossy surfaces
Complex geometries
Applications requiring homogeneous illumination
In Summary; Thanks to advanced optical components, polarization techniques, and filter management, we can completely neutralize the disruptive effects of ambient external light and highlight micro-level details with high contrast. When the right balance of wavelength, diffusion, and collimation is established, it is possible to achieve a stable and repeatable quality control mechanism, even in the harshest production environments.
Now that we have unlocked all the physical and optical secrets of lighting, it is time to move on to the lead actors that will capture this flawless light and transform it into digital data.
In the next part of our series, we will put the intricacies of Industrial Camera Types and Lens Selection—which will work seamlessly integrated with these optical setups—on the table. Stay tuned!