LED lighting for machine vision applications, including wavelength, pulse mode, polarization, incident angle, and technique, is the most important consideration when creating a machine vision solution. Today, the vast majority of machine vision lighting systems use solid-state, or light-emitting diode (LED), technology because it consumes less power, generates less heat, is more compact, and is more efficient than incandescent, fluorescent, or gas discharge light sources. Unfortunately, LED lighting for machine vision applications too often is a late consideration, which can lead to wasted effort and excessive costs. A simple example is deploying a color camera costing twice as much as a monochrome grayscale camera rather than using low-cost filters to convert color data into intensity data that can be measured by more cost-effective monochrome cameras. Another example is using a laser scanning system for 3D triangulation, which requires additional safeguards to protect nearby workers, rather than using photometric or computational imaging approaches with eye-safe LED lighting.
LED Lighting for Machine Vision Applications
Machine Vision LED Lighting
With the advent of ultra-high-brightness LED dies that last many times longer than traditional incandescent or fluorescent light sources, machine vision LED lighting came to quickly dominate the manufacturing and industrial lighting industries as a source of photons for imaging applications. Machine vision LED lighting offers a number of benefits for designers, including the ability to select specific wavelengths of light with narrow bandgaps, to deploy high-brightness sources in compact retrofit application areas, and to avoid electronics and light sources that generate excessive heat. In addition to using micro-lens arrays, diffuser panels, bar optics for line lights, and other optics, designers can choose exactly the right color and direction of light to work with an application, regardless of whether it’s in automation, durable goods, electronics, food processing, packaging, or any of the hundreds of other industries served by machine vision LED lighting solutions.
Machine Vision Lighting Techniques
Machine vision lighting techniques include brightfield or direct lighting, darkfield or indirect lighting, backlighting, and diffuse lighting. Brightfield or direct illumination is the most common lighting technique: the light and camera are both placed in front of the object under test; light from the source reflects off the object under test and is collected by the sensor in the camera. Darkfield techniques place the lighting at a large angle compared to the optical axis between the sensor and the object under test, resulting in reflected light not reaching the sensor and revealing 3D surface features. Back lighting, another common machine vision lighting technique, generates exceptional contrast by creating dark silhouettes against a bright background. The most common uses are detecting the presence or absence of holes and gaps, part placing or orienting, and measuring objects. Finally, with diffuse lighting, which is a version of brightfield lighting, integrating spheres or other secondary surfaces reflect light back onto the object under test, creating light that essentially comes to the object from all sides and directions, reducing hot spots and other problematic conditions for machine vision solutions.