ADVERTISEMENT FEATURE Optical inspection
WHEN THE CAMERA GETS IT WRONG:
...the cost of optical compromise in automated inspection, by Knight Optical
provided the optics are specified to capture clean spectral data in a demanding industrial setting. UCL research published in 2025
M
achine vision is now standard in manufacturing inspection, with Gartner forecasting that by 2027, half of all
warehouse operations will use AI-enabled vision systems in place of traditional scanning-based cycle counting. The optical components within these systems determine data quality, and poor data leads to poor decisions no matter how advanced the downstream processing is.
Automated optical inspection (AOI) operates under inconsistent conditions: natural light shifts through the day, industrial ceiling lighting is harsh and directional, and many manufactured surfaces are reflective. This creates unwanted light reaching the sensor alongside the signal the system is trying to read.
Inconsistent illumination can cause intensity variations, poor repeatability, and colour mismatches, while reflective surfaces generate stray light that obscures fine detail. In food sorting and pharmaceutical inspection, this leads to missed defects and undetected contamination, as well as the inverse problem of false rejects, where good product is discarded unnecessarily, creating waste and hurting yield. The solution is spectral control at the component level. Interference bandpass filters transmit only a defined wavelength range and block everything else, including ambient light from overhead sources. Matched to a system’s LED illumination, they stabilise exposure across variable conditions and maximise contrast on the inspected item, helping flaws, colour deviations, or dimensional anomalies stand out against the background.
automationmagazine.co.uk
Filter specification affects real-world performance: broadband filters suit general QC environments prioritising light throughput; narrowband filters perform better under high ambient interference; standard filters match common LED wavelengths for most setups; and UV filters detect fluorescence and coating layers invisible to the naked eye, relevant to pharmaceutical and security applications.
The cost of misclassification A mis-specified bandpass filter compromises the system’s ability to make reliable decisions: equipment slows on ambiguous data, false reject rates climb, and defective product can occasionally pass through. In automotive manufacturing, a missed weld defect can mean a recall; in pharmaceuticals, an undetected contaminated blister pack carries regulatory and patient safety consequences; in food and drink production, an undetected foreign body can trigger a product withdrawal. The integrity of the inspection result is directly tied to the optics.
Engineers specifying these systems understand this, but the point can be lost when component selection is treated as procurement rather than a technical decision. A filter that’s close to spec but not exactly right for a facility’s ambient conditions will produce subtly degraded results. This is not always obvious in testing, but cumulative over a production run.
Beyond pass/fail inspection, material identification at high throughput introduces more complex optical demands. In recycling automation, hyperspectral imaging (HSI) systems scan conveyor lines at speeds up to 3 m/s, identifying polymers (PET, HDPE, PVC, polypropylene, polystyrene, and ABS) by their distinct spectral fingerprints in the near-infrared (NIR) and short-wave infrared (SWIR) regions,
demonstrated contaminated plastic packaging identification at up to 97% accuracy using HSI, illustrating both the technology’s potential and how much optical quality determines whether that potential is realised in practice. At these conveyor speeds, components need high transmission to make sure enough light reaches the sensor during short integration times. Shiny mixed-material surfaces create stray reflections and flare; bandpass filters isolating target NIR and SWIR wavebands block this interference and keep readings clean. The same spectral control principle stabilising standard AOI lines applies here, under more demanding conditions. AOI equipment runs continuously and is subject to thermal cycling, UV exposure, vibration, and abrasive cleaning agents. Optical components that degrade under these conditions impact the inspection result. Diamond-like carbon (DLC) coatings
provide abrasion resistance for components subject to regular contact or cleaning; dielectric coatings offer thermal stability under temperature cycling; and protective windows, typically sapphire for its hardness and optical transmission, shield internal components from dust and impact, maintaining the optical path as installed. A well-specified optical setup produces cleaner data, faster and more reliable decisions, lower false reject rates, and an inspection result that lasts the equipment’s operational life. Knight Optical supplies precision optical components for automated inspection and machine vision applications across manufacturing, food and drink, pharmaceutical, and recycling sectors. The range includes interference bandpass filters, protective windows, custom-engineered optics for demanding environments, and support through specification to ensure components match real operating conditions.
Knight Optical
www.knightoptical.com
Automation | June 2026 27
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