ABSTRACT
Electric lighting serves as a benefit for the people who experiences the electricity distribution systems: first as street lighting, then as lighting in theatres, hotels, shops and home. The propagation of light is either 'arrival of light' or 'illuminance'. The luminous efficacy of a source is the ratio of the luminous flux emitted by a luminous source to its input power and is measured in lumens per watt. Light arriving at a surface is called incident light and when this light is not perpendicular to a surface it strikes, then illuminance is subjected to the cosine law. The inverse-square law is applied when the surface being illuminated is perpendicular to the incident light, it strikes. The chapter deals with the energy level of individual electrons that determines the shell they occupy and those who have the greatest energy levels. Whenever an electron changes its energy level and moves between shells, it either emits or absorbs photons.
