Light is a invisible form of energy that causes the sensation of vision. 

 

Those bodies which emit light in all directions are called sources of light. The sources can be point one or extended one. The sources of light are of two types :

Those bodies which emit light in all directions are called  sources of light. The sources can be point one or extended one. The sources of light are of two types :

Eg : Sun and stars (natural luminous sources), electric lamps, candles and lanterns (artificial luminous sources).

                                    

 

 

(ii) Non - luminous sources : Those objects which do not emit light but become visible only when light from luminous objects falls on them. They are called non - luminous sources. 

Eg. : Moon, planets (natural non - luminous sources), wood, table (artificial non - luminous sources) etc. 

 

 

 

 

· Bioluminescence: The production or emission of light by a living organism as a result of some chemical energy getting converted into light energy is called bioluminescence. The name originates from the Greek word bios for 'living and the Latin word lumen for 'light'. Fireflies are insects that give off a pale, greenish yellow light that flashes or glows in the dark . Some of the fish, such as angler fish, living deep under the sea are also bioluminescent. 

                                         

Substances through which light propagates or tends to propagate is called a medium of light.

According to the medium of light objects are divided into three parts :

Bodies that allow light to pass through them i.e. transmit light through them, are called transport bodies. 

Eg.: Glass, water, air etc.

                                

(ii) Translucent object : Bodies that can transmit only a part of light through them are called translucent object. 

Eg.: Frosted or ground, greased paper, paraffin wax etc. 

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