Let the light change life
In electronics manufacturing and semiconductor packaging, automated optical inspection (AOI) has become an essential part of quality control. An AOI system's inspection accuracy depends on three factors: camera resolution,algorithm capability, and lighting quality. The first two get most of the attention. Lighting is often the last thing people think about. But anyone who has actually tuned an AOI system knows — more often than not, the bottleneck isn't the camera. It's the lighting.
The AOI light source market was valued at approximately $1.21 billion in 2025 and is projected to reach $2.28 billion by 2032, with a compound annual growth rate of 9.44%. Lighting is gradually shifting from being a supporting component in AOI systems to a key driver of inspection efficiency.
Let's go through a few situations that AOI engineers have probably all encountered.
Non-uniform illumination. If the lighting system doesn't deliver uniform illumination across the inspection surface, the camera picks up images with bright and dark areas. On the same board, the bright areas look normal while the dark areas look like defects — and the algorithm struggles to tell whether it's a real defect or just uneven lighting. Poor uniformity in illumination brightness directly affects photoelectric conversion and subsequent image processing. The result is false positives on good parts and missed defects on bad ones.
Glare from highly reflective surfaces. Solder joints on PCBs, metal pins on chips, glass substrates — under conventional lighting, these materials produce strong specular reflections that show up as bright spots in the image. Anything under those bright spots is completely obscured. Specular reflection from complex material surfaces is a long-standing challenge in AOI. Glare tends to cause false positives, while shadows tend to cause missed defects — neither is acceptable.
Shadowing. When the lighting comes from a single direction or at the wrong angle, the raised structures on components cast shadows that obscure critical features like solder joint edges or pin roots. The smaller the component, the more pronounced the problem.
Thermal effects. Traditional light sources like halogen lamps generate significant heat. Prolonged exposure can cause PCBs to warp slightly or the performance of precision component solder joints to drift. The objects being inspected are precision electronic assemblies — thermal effects cannot be ignored.
Ambient light interference. The ambient light around AOI equipment is never constant — it changes between day and night, between sunny and overcast days, and when nearby equipment turns on or off. Natural light fluctuates throughout the day, and industrial ceiling lights are both harsh and directional. These uncontrollable variables can cause the same product to yield different inspection results at different times.
Fiber optic lighting in AOI systems isn't meant to replace LEDs. It's meant to solve the problems that LEDs and traditional light sources can't handle. Several characteristics of fiber optics directly address the pain points mentioned above.
Flexible light guidance. The light source sits in one place, and the fiber delivers the light where it's needed. Space inside an AOI machine is already tight — cameras, lenses, and motion mechanisms take up most of it, leaving very little room for lighting. Fiber optics can route through tight spaces and around corners — something rigid lighting fixtures can't do. Some fiber optic lighting systems achieve extremely small bend radii, making cabling straightforward.
Cold light illumination. Fiber optics transmit light with virtually no heat generation. The light that comes out of the fiber end is cool. This means PCBs don't warp from heat, solder joint performance doesn't drift, and inspection results are more stable.
Uniform illumination. Through proper fiber bundle arrangement and light mixing design, fiber optic lighting can achieve high uniformity across the output surface. Whether it's linear or ring light, the uniformity can be consistently high. Uniform lighting means the algorithm deals with stable, consistent images — and false positive rates drop accordingly.
Multiple light patterns from a single source. The same light source can produce ring light, linear light, area light, or spot light simply by swapping the fiber bundle. Coaxial fiber optic illumination can achieve 360-degree uniform lighting, virtually eliminating shadows. Different angles of light reveal different types of defects — scratches show up best under side lighting, surface contaminants are easier to spot under diffuse lighting, and edge contours need low-angle light to stand out.
Enclosed light path. Fiber optic lighting systems are enclosed from the light source to the output end, unaffected by external ambient light. Whether it's day or night in the workshop, whether nearby equipment is on or off — the lighting conditions remain consistent. This greatly improves the repeatability and comparability of inspection results.
In actual AOI inspection, fiber optic lighting is used in several specific areas:
PCB and FPC inspection. Linear fiber optic light guides paired with line scan cameras provide high-intensity, high-uniformity linear light sources for continuous inspection on high-speed conveyor lines. When ultra-long linear light is needed, a specialized One into more outlet optical fiber assembly allows a single high-power illuminator to deliver balanced light across multiple output branches, or conversely, accept multi-branch inputs to feed a single light guide. With cylindrical focusing lenses and diffusers, the light density and uniformity can be further improved.
Semiconductor wafer inspection. Ring fiber optic light guides paired with microscope lenses provide coaxial illumination that minimizes shadows and highlights surface defects. Light projected uniformly from around the lens is particularly effective for detecting minor defects on mirrored or highly reflective surfaces. For semiconductor packaging inspection requiring dual-direction lighting, dual-branch fiber optic bundles are available. In tight spaces where mounting is difficult,metal tube fiber optic light guides offer a good alternative.
Multi-station inspection. A single light source can feed multiple fiber bundles, distributing light to different stations. This reduces equipment costs and simplifies cabling.
Highly reflective surfaces. Metals, glass, and other strongly reflective materials tend to produce glare under conventional lighting. Coaxial or low-angle illumination can suppress specular reflection and make defects clearly visible in the image.
Flexible and curved surface inspection. FPC flexible boards have uneven surfaces that rigid lighting struggles to cover uniformly. Fiber optics can conform to curved surfaces, providing more consistent illumination.
In practice, fiber optic lighting and LED lighting each have their place. It's not a matter of one replacing the other.
Fiber optic lighting excels in flexibility — changing the light pattern is as simple as swapping a fiber bundle, without replacing the entire fixture. It adapts easily to tight installation spaces thanks to flexible light guidance. Its cold light feature is irreplaceable in heat-sensitive applications. Multi-station expansion is straightforward — one light source can feed multiple points. The downside is that the initial cost is slightly higher than basic LED solutions.
LED lighting has a lower initial cost and works well for standard scenarios that don't require specialized light patterns. However, the light pattern is fixed, replacement costs are higher, and heat dissipation is a concern.
In short, when the inspection scenario demands specific lighting angles or patterns, or when the sample is sensitive to heat, fiber optic lighting is the better choice.
How to choose the light pattern. Linear light pairs with line scan cameras — integrated with a high-uniformity Display Lighting Fiber Optic Cable, it is ideal for the continuous, high-speed inspection of PCBs, FPD modules, and glass substrates. Ring light provides coaxial illumination — eliminates shadows, suitable for mirrored and highly reflective surfaces. Area light provides large-area uniform illumination. Spot light provides pinpoint illumination for precision features.
How to choose the fiber material. Quartz fiber offers high transmission efficiency (over 95%), a broad spectral range from UV to IR, and good temperature tolerance — suitable for applications with demanding optical quality requirements. Glass fiber offers good value for money — suitable for regular visible light inspection. Plastic fiber has the lowest cost and best flexibility — suitable for short-distance, low-cost applications.
How to determine length. Length should be based on the routing path inside the machine. Standard lengths typically range from 1 to 5 meters, with special applications up to 10 meters. Longer lengths mean higher transmission loss — long-distance applications require consideration of end-face attenuation and low-loss fiber.
How to match the connector. SMA905 is the most common fiber interface standard in the AOI field. Before selecting, confirm the interface type of your existing light source to ensure compatibility.
Hecho Technology has been working in AOI fiber optic lighting for years, offering linear, ring, and area fiber optic light guides with full customization from light source to fiber bundle, including OEM and ODM services. Linear fiber optic light guides are available with illumination areas ranging from 50mm to 1260mm. Ring fiber optic light guides come in various diameters and output angles. All products use imported high-transmission fiber materials.
As AOI inspection precision requirements continue to rise, fiber optic lighting — with its flexible light guidance, cold light, and pattern versatility — is well positioned to solve many long-standing lighting challenges. If you're dealing with non-uniform illumination, glare interference, space constraints, or thermal effects in your actual tuning work, fiber optic lighting is worth considering as a serious option.
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