What is the Ruduce Power Emergency Converter for Emergengcy Lamps?

What is the ruduce power emergency converter for emergency lamps? For example, there is a popular 24 watt ceiling lamp. When we connect it to the city power, and turn on the switch, it works in the 24 watt. If we want to chanage it into an emergency light, we need to install a 5-50 watt emergency power supply for it, it will become an emergency light immediately. When the city power supply is available, it works as an ordinary 24 watt ceiling lamp. When the power supply is no available, it will turn to the mode of emergency working automatically, and it’s brightness same to the normal 24 Watt celing lamp. If we install a reduced power emergency module for it, for example, we install a reduced power emergency inverter module. When the city power off, it turn to the emergency working mode, it’s brightness is only about the brightness of a 5W light. 24 watt down to 5 watt, so we call this kind of emergency power pack as reduce power emergency power supply or reduce emergency power converter.