There are two sources of light natural and artificial. Nearly all natural light is received from the Sun.
Artificial light is light such as that pro-duced by electric lamps, fires, or fluorescent tubes.
Luminous bodies are those bodies which pro-duce their own light, such as the Sun and the stars. Illuminated or nonluminous bodies are those bodies which merely reflect the light they receive and are therefore visible because of this reflec-tion. The Moon is an example of an illuminated body. Theory When light is emitted from a source, waves of radiation travel in straight lines and in all directions. A simple example of motion similar to that of radiation waves can be seen by drop-ping a pebble into a pool of water.