We know Sun is main source of light in our life . Our whole ecosystem depends on sun. Light has has a wide range of specturm some are visible and other are not to our naked eyes.

So if we have sun and moon to provide light why do we need artificial source of light? 

Well we require artificial light for our application of work.

Lets start

1. General lighting: This is required to have basic amount of light in your house or building. Eg we use Tubelights and surface lights for it and wattage required is also not more. It varies based on indivdual requirement.
2. Task lighting:This type is used when you want to perform specific task. Eg Table lamp is required if you are sitting on study table.In Daimond industry they use high wattage T5 since their work is very minute.
3. Landscape lighting: This is done to lit up Garden and Porch.We use spike lights, Bollards, Gate lights ,Wall washers for beautification.
4. Outdoor Lighting: This is for protection of premises and lighting outdoor areas like roads. Eg Streetlight is used for outdoor light and Flood lights are used in stadium.
5. Mood lighting: This is used to create theme. eg Use Rgb lights with remote in home theater or bar room to create a soothing atmosphere. 
6. Special application lighting:we have plant lights which are used as artificial source of light for growing plant where sunlight is not available. Aquarium light is used for fish development. Ultraviolet and infrared lights used in submarines, boats and pharmaceutical industries.
7. Underwater lights: Used to light up water bodies like swimming pool and fountain.
8. Stage lighting: Used in events . We can see its application in Reality shows.The lights have moving head. 
9. Automobile lighting: head and tail lights of car .                                                  Now lets see how the lights work.They work on AC i.e 220v directly the voltage we get in our house or DC stepped down and converted by transformer it is constant voltage having general value of 12V or 24V. Device working on DC have less chances of getting affected since voltage fluctuation is not there and thus have longer life.Always while purchasing light keep in mind the current and voltage combination on  any lighting device. Also keep in mind power factor it is indicator of efficiency of driver and load factor. 
   Thanks for reading. I am in this feild since 2009 and have industry experience of 12 years. 
   We have done projects on above concepts inGSFC,IOCL, Sun Pharmaceuticals, Alembic Pharma