Standard LED lights are offered in a wide range of shapes, sizes, working distances, coverage areas, wavelengths, and lighting techniques. There is generally an “ideal” lighting configuration for your specific application.
With literally thousands of choices, R.J. Wilson, Inc. and its lighting partners have the real-world experience and technical know-how to help you select a lighting configuration that is optimized for your application requirements. Let’s discuss the options available. Lighting is the most important aspect of a machine vision imaging system, so it’s worth the upfront work to evaluate the lighting to be sure it’s a proper match for the application.
The goal is to select a lighting technique, position, and shape that properly illuminate the object to make the features-of-interest, edges, or regions reliably and repeatably visible to the inspection software.
Spectrum Dome, AI Backlights, AI Bar, AI On-Axis, CCS FPQ, CCS Ring, SVL Brick
Download this document for an overview of the available lighting form factors and how light delivery formats can affect the appearance of objects.
Available LED wavelengths range from the ultraviolet, through the visible colors of the rainbow, and into the infrared range. The selection of a wavelength depends on numerous application factors, with the goal being to acquire an image that makes it easier for the vision software to do its job by making features-of-interest easier for the vision software to “see”.
For visible light imaging, the LED color can be used to make the features-of-interest or defects more visible to the vision system, based on how they reflect or absorb light of various wavelengths.
Download the document below for an overview of the effects of UV, visible, and NIR LED wavelengths on the appearance of objects in the acquired image.
When using a monochrome camera, the selection of the LED wavelength is sometimes dependent upon whether a specific color feature in the object needs to be enhanced or diminished. The use of an LED color close to the object color will lighten its appearance in a greyscale image. The use of a color on the opposite side of the color wheel from the object color will darken it.
UV wavelengths are typically used to cause an object, such as the printing on the tamper seal below, to fluoresce in a visible wavelength. The same effect is seen when invisible ink is exposed to UV light – it emits light at a visible wavelength, such as 635nm red. A bandpass filter is used on the camera lens to pass only the visible wavelength at which the sample emits. This reduces the amount of “bluish” UV light that is included in the captured image and enhances the emitting wavelength of a tamper seal, an adhesive, a plastic, or other material.
Newer UV lights from CCS, known as “Pure UV”, further minimize the amount of visible light produced by the UV LEDs, enhancing the detection or reading of UV codes or features.
In the example below, the printing on the tamper seal is glowing at a visible wavelength when illuminated with UV light. The presence of the printing is used to verify the tamper seal is present.
UV Light Causes the Printing in the Tamper Seal to Glow in a Visible Wavelength
When an optical brightener is added to the object’s production materials, UV lighting can be used to verify its presence, since it will glow in a visible wavelength when present. This may apply to tamper bands, inks, adhesives, plastic parts, or other objects.
NIR light is more effective at penetrating certain materials than visible wavelengths. Near-infrared light’s longer wavelength often allows for less scattering from part surfaces and higher transmission rates through them. Higher transmission means the NIR light can pass through more materials, making it ideal for inspecting for part presence within packaging, detecting fill levels, or imaging foreign matter.
IR Light is Used to View Through the Printed Package to See the Ear Plugs Inside
In the image below, white light is used on the left and near-infrared light is used on the right. The NIR light is not reflected from the printed date code, permitting the vision system to see and inspect only the object underneath.
White Light Shows the Date Code, Near-Infrared Lighting Passes Through the Printed Code
NIR light is effective at neutralizing or reducing contrast differences based on color in monochrome images, primarily because the reflection of NIR light is based more on sample composition rather than color differences. This property can be used when less contrast or the reduction of the effects of color is desired.
Near Infrared Light Can be Used to Diminish the Greyscale Differences Between Color Objects