You could try setting a bool in your day/night cycle like ‘IsNight’ and check that on your lamp. If it’s not night, the lamp is off. Otherwise it’s on.
If you check the sample content there’s a level called BlueprintOffice that shows how to use Event Notifiers. You could set one of those up so that night and day send events that all your lights could catch. I honestly don’t remember how that is set up, but take a look at how the automated camera interacts with the alarm system. You might be able to do something like that with your lamp and day/night.