In today’s world we require high speed internet to access websites and mobile applications. And to access that, on an average we get 2-4mbps speed. Over that when more and more users join the network, speed of internet gets divided into then and speed gets slow. Imagine a person standing in the middle of street and want to access internet, how he can access it- by using free wi-fi if available or by mobile data. But the range of mobile network maybe not available there and if there is no mobile network how one can imagine free wi-fi. Till date one cannot imagine internet under water. There are few sensitive areas like hospitals, aircrafts where use of radio waves are not allowed, then if is difficult to access internet in these conditions.So, to above problems Phycist .Harald Haas has come up with a solution he calls “data through illumination” or Li-Fi . In this paper, we will discuss Li-Fi technology in detail and also discuss how Wi-Fi can be replaced by Li-Fi.