Streetlights on/off light pollution impact

Does anyone know how much streetlights affect light pollution? I live an hour East of London, goodtostargaze says Bortle 6.2, but my counties' streetlights turn off at 1am. Anyone know how much this would impact light pollution? I want to get a 6" Dob (Stellalyra) and cant really go to dark sites at the moment because I can't drive, so want to get a rough idea of what I'd be able to see in terms of DSO.

Thanks!