There are some applications where light needs to be focussed into a point or along a line. The main uses for this technique are to either concentrate the light into a smaller area, thus increasing its intensity such as would be the case for high-speed applications, or to illuminate only a specific part of an object.
A common application for this technique would be a line scan web inspection, where a thin, highly focused beam of light is required across the whole width of the web. The illumination must be able to provide high intensity, even illumination for the line scan camera.
The normal method would involve using an array of high intensity LEDs to provide very uniform illumination along the line. A focussing/rod lens is then used in front of the LEDs to focus the light to a fine line.
Another reason to use a focused light is to control how the light strikes the target. The example of an inspection of pins on an electrical component shows this in action.
Using this technique, the main body of the component is not illuminated and the focused beam only illuminates the electrical contacts. This makes the sub sequent inspection much simpler as there is no extraneous information in the image that would otherwise need to be removed in software.