Luminiscence: The emission of light during a process other than by the action of heat i.e. emission of cold light is called Luminiscence. This can be of following different types:
1. Chemiluminiscence:
The emission of cold light during a chemical reaction is called Chemiluminiscence. For example: flow worm i.e. fire fly glows due to oxidation of protein, luciferin present in it. The glow thus produced in the living organisms is called bioluminescence.
2. Fluorescence:
Some substances when exposed to light absorb it and immediately start re-emitting it. The glow continues so long as the light falls on the substance. The glow continues so long as the light falls on the substance. The flow thus produced is called fluorescence and the substances producing the glow are called fluorescent substances e.g. fluorite (CaF2).
3. Phosphorescence:
Some substances like ZnS continue to glow for some time even after the light is cut off. Such substances are called phosphorescent substances and the phenomenon is called Phosphorescence.
