Our combined power generation and distribution is just under 16¢ per kWh.
Our ceiling lights are all 6" - 12w Dimmable LEDs, so if my math is right, that is 12 watt-hours of usage, operating say, 8 hours per day would be 96 watt-hours, or .096 kWh per light.
At 15.793 cents per kWh, that's 1.58 cents per day for each light left on for 8 hours. A room with 4 overhead lights would cost just over 6 cents if left on all night.
It seems hardly worth disquieting a 50 year relationship over 6 cents...
So growing up in the same house with my "Great Depression" Grandparents, I quietly turn off the unneeded lights that I find, and just go on my way without saying anything.
...Pick your battles wisely...