I've never really thought of it before, but is there an official rulling on whether players without darkvision can see when outside at night in an open area? I'm not sure if moon light would be enough to see or not.

It's referenced under the "vision and light" rules. When talking about dim light, it says "A particularly brilliant full moon might bathe the land in dim light." Dim light means lightly obscured, which has associated rules for sight.

Yeah, a well lit night would be dim light. Disadvantage on perception (for those without darkvision) but not for attacks.