Some of the common illumination sources are tungsten, quartz halogen, quartz iodine, fluorescent, and mercury or xenon arc lamps, as well as various flash lamps, lasers and LED sources. The common ways to configure these sources are: 1) illumination of the scene, 2) backlighting (shadowing) of the scene or 3) a combination of both, depending on the type of information desired from the camera.
The light intensity required by the image sensor must be well defined in order to have even illumination of the scene, since the camera uses a common threshold for the entire scene, calling it light or dark. Only a small portion of light from the light source, via the scene, actually ends up in the sensor. Therefore, in choosing a suitable light source, such factors as even illumination versus threshold, f-stop and magnification of the lens, and the surface of the object (light or dark, diffused or specular) must be considered. Certain sections of the object may require spotlights to create an even illumination where a meaningful threshold scene can be produced. The amount of light coming through the lens is increasingly attenuated as the angle between the center of the lens going to the edge of the lens increases.