A built-in flash is a light source that is an integral part of the camera body. Its main task is to illuminate the photographed scene in conditions where there is a lack of natural or ambient light, for example, indoors or at night. It can also be used on a bright day for what is known as "fill flash," when it subtly brightens dark areas on a face or object that are created by harsh sunlight. Compared to external flashes, which attach separately to the camera, it usually has lower power and more limited settings options. Due to its placement close to the lens, it can sometimes cause the red-eye effect in portrait photography, which is a reflection of light from the retina.