You probably already know this but the lights coming on after power outage is just a factor of that device technology, not something to do with SmartThings. But I like your idea of knowing that the power came back on.
I’m not sure the hub going off is the right answer, though, since the hub can go off independent of any circuits that the lights are on. In fact it could just be lost Internet connectivity which won’t change the brightness of the lights.
There are some people who were monitoring for power outages using any of several devices which show energy draw. But one that I think is the most clever is the original generation smartthings motion sensor. This device can run either from USB power or from battery. So a couple of members have captured the moment when it changes from battery powered to USB power as an indicator that power has returned to the circuit. Like I said, very clever. I particularly like the fact that this is catching the power on moment rather than the power off moment.
So that’s one option that is available today, although it does require the additional device.
Here’s one use case example from @scottinpollock using code from
Jesse Ziegler:
This is awesome! Power is Out based on state of v1 Motion Sensor