Fluctuating ambient light is one of the most common causes of false rejects in image processing. While high-contrast tasks can be protected with narrow-band optical filters and powerful flash lighting, high-precision surface inspections and colour analyses require complete mechanical enclosure via an inspection tunnel.
The physical risk of uncontrolled ambient light
Industrial camera systems evaluate absolute brightness and contrast transitions (grayscale) in the digital image. If the ambient light in the production hall changes – for example due to shifting sunlight through roof lights, changing cloud cover, or hall lighting switching on at shift change – these baseline values shift uncontrollably. A statically defined threshold for defect detection then inevitably leads to incorrect decisions (false rejects or undetected defective parts slipping through).
Level 1: Optical filter technology (narrow-band filters)
If the camera system's internal lighting operates at a defined wavelength (e.g. monochromatic red light at 630 nm or infrared at 850 nm), a matching bandpass filter is screwed onto the camera lens. This blocks the entire spectrum of visible daylight and hall lighting and lets through only the light from the system's own illumination. This is the most efficient method for simple contour and dimensional inspections.
Level 2: Overdrive flash and extremely short exposure times
The LED lighting is driven to extreme brightness for a few microseconds (e.g. 20 µs) via a high-power flash controller. At the same time, the camera's exposure time (shutter) is set precisely to this short time window. Since continuous hall lighting contributes almost no energy to the sensor within these 20 µs, it becomes nearly completely invisible in the image.
Level 3: Mechanical enclosure (the THOPinspect inspection tunnel)
For demanding high-end surface inspections (e.g. detection of the finest scratches, gloss-level differences or complex colour measurements), filters and flash techniques reach physical limits, as ambient light reflections visually overlay the surface structure. In these cases, complete optical isolation is essential:
- Constant lighting environment: Complete independence from external light disturbances in 24/7 operation.
- Combination of perspectives: Enables the simultaneous, undisturbed use of bright-field, dark-field and coaxial lighting in a single station.
- Protection of the optics: The enclosed tunnel also protects camera sensors and sensitive optical filters from contamination, dust and accidental misalignment.
The modular THOPinspect Tunnel concept offers a turnkey solution that can be integrated directly into your production line. This completely eliminates the risk of ambient-light-related false rejects from the outset.