In regards to image processing, the choice of the right illumination is essential. The sentence 'Good illumination, good machine vision' should be a reason to think thoroughly about the right illumination for the machine vision task ahead. With the EyeLight series, EVT provides industrial lighting for almost every application, including a selection of dark-field illumination, such as the EyeLight LLA series. These are available as RGB model or in their separate colours: red, green, blue or white.
The dark-field ring lights are available in different inner- and outer-diameters. The inner-diameters vary from 40-136mm and the outer-diameters vary from 74-174mm. The LLA series is compact, with only 20mm of body height. It works best with working distances ranging form 5-10mm. Optionally there are also diffusion filters and polarisation filters available.
The rays of the dark-field illumination are refracted from the object, therefore not all light rays reach the camera lens directly. Typical applications for dark-field illuminations are edge detection and the inspection of embossed imprints or errors such as scratches on metal or other shiny surfaces.
The advantage of the LLA dark-field ring light is that reflections are avoided. With the flat angle of reflected the light is suitable for applications of slightly uneven surface structures or engravings on metal surfaces, etc. The uneven surfaces and edges of a coin or a button cell are illuminated clearly as well as scratches on the surface.
The example images show the LLA dark-field ring light with a 1¢/EUR coin and a button cell. The edges and errors are clearly visible.