Li-Fi is a high speed and more advance internet connection system then Wi-Fi which used LEDs as means to provide service.
It is based on Visible Light Communications (VLC) in which data is transmitted through LEDs, this means that LED should be on to consume data and use internet but the light can be dimmed so that it will not be visible by human eye.
It is very successful in places where the electromagnetic interference was considered dangerous such as nuclear power plants, aircraft cabins and similar areas. Wi-Fi uses radio waves to transmit data which makes it dangerous while Li-Fi used visible light.
Li-Fi if fully developed will be a faster mode of network than WiFi and some believe that Li-Fi will make WiFi a part of history just like Bluetooth made infrared history.