If the FRITZ!Box loses power, all of the settings of the LED light FRITZ!DECT 500 for brightness and color are retained. The LED light remains on or off, depending on its state at the time when the FRITZ!Box lost power. Automatic switching of the LED light, for example switching schedules, will not function.
As soon as power is restored to the FRITZ!Box, it will once again be switched automatically. If you configured a specific switching state for the LED light after a power failure on the "Light setting" tab in the menu "Smart Home > Device Management" or "Devices and Groups" of the user interface of your FRITZ!Box, this switching state will be activated after the restart.
If there is an internet failure, the LED light can still be switched within the home network.