text: Assist lamp The assist light (also known as AF illuminator) "activates" passive autofocus systems in low-light and low-contrast situations in some cameras. The lamp projects visible or IR light onto the subject, which the camera's autofocus system uses to achieve focus.
  Many cameras and nearly all camera phones lack a dedicated autofocus assist lamp.  Instead, they use their built-in flash, illuminating the subject with bursts of light.  This aids the autofocus system in the same fashion as a dedicated assist light, but has the disadvantage of startling or annoying people.  Another disadvantage is that if the camera uses flash focus assist and is set to an operation mode that overrides the flash, it may also disable the focus assist.  Thus, autofocus may fail to acquire the subject.
  Similar stroboscopic flashing is sometimes used to reduce the red-eye effect, but this is only intended to constrict the subject's eye pupils before the shot.
  Some external flash guns have integrated autofocus assist lamps that replace the stroboscopic on-camera flash.  Many of them are red  and less obtrusive.  Another way to assist contrast based AF systems in low light is to beam a laser pattern on to the subject.  The laser method is commercially called Hologram AF Laser and was used in Sony CyberShot cameras around the year 2003, including Sony's F707, F717 and F828 models.