A gigantic source of light in the sky that lights up a part of the Earth and is too bright to look at is... the sun. I think we're all used to the sun.
If one person owned the sun and could charge all humanity for access to its light then maybe that would be a relevant example
everyone’s seen ads before, mind if I put a giant ad in the sky for everyone to look at?
I personally am _not_ used to seeing the sun after sunset and before sunrise.