How to gently remind tenants to turn off the lights?

According to a person's usual habitual tone, it is generally understandable to say to each other like a normal greeting. "Can you turn off the light?" According to my personal habits, I usually tell people "Dear XXX, and then add what I want to express" in an exaggerated way. I'll say the same thing. Personally, I think it would be better to express my feelings directly, but pay attention to the expression of language. It is not easy to have some unnecessary guesses and troubles directly, so that others can feel the joy of being respected, and then you can praise each other in a very light tone. Don't worry about embarrassment.