Most likely reason for this wouldn't be a power outage imo... most likely a blackout. Blackouts and curfews were very common in WWI/WWII so as to avoid air attacks from both the axis and the allies. Families would have to hang heavy dark curtains, and at dusk, they would be required to close the curtains tightly to ensure that no light could be seen from the outside, making it extremely hard to drop bombs onto cities and military bases.

Regards,
Ayrus