When you turn the light off, say to yourself "the light is now off", then step away and do not go back to check, even if your brain wants you to. Tell your brain that you can accept whatever the consequences are, and that there won't be any because you turned the light off. For cleaning, set a day to do one deep clean (maybe once a week) and only do surfaces daily. Tell your brain that that is enough, you know what it wants you to do but you are not playing it's games. OCD is like a bully so treat it like one. The sooner you ignore the bully, the sooner it leaves you alone. Good luck.
Thank you very much I really appreciated it
sometimes I just want to take a screenshot of the light
You can do that maybe, but only look at it once and then delete it. Then you're giving your brain the reassurance once and telling it "no more, now I have told you". I have Harm OCD and when my brains kicks in sometimes I like to laugh at it. I will say "uh huh, sure" to show it I do not take it seriously. Also try giving the bully a name. I call mine Aragog, like from Harry Potter. I do not know why, it was just the first name that came to me haha