Rays of light and light sources
Light and its associated manifestations, such as shadows, the colors of objects, and the images produced by mirrors and lenses, are studied in an area of science called optics.
The sun, a burning candle, and a lit light bulb are examples of light sources, ie, bodies that emit light. Light sources are seen when the light emitted by them reaches someone's eyes.
The figure below shows the light rays emitted by a candle. These rays are emitted in all directions, which is why we can see the same lighted candle from wherever we are in the room.
Rays of light and illuminated bodies
In total darkness it is not possible to see objects that do not emit light, such as a pencil, an unlit lamp, or a sheet of paper. We can only see them if they are struck by light rays from a light source, ie if they are illuminated. When light rays from a light source strike an object, illuminating it, some of these rays may be reflected. The object is seen because these reflected rays reach someone's eyes, as the following drawing shows.
Independence of light rays
The rays of light from one light source do not interfere with the propagation of rays from another light source, even though their path crosses. This is known as principle of independence of light rays.