Abstract—This paper is about localising at night in urban environments using vision. Despite it being dark exactly half of the time, surprisingly little attention has been given to this problem. A defining aspect of night-time urban scenes is the presence and effect of artificial lighting — be that in the form of street or interior lighting through windows. By building a model of the environment which includes a representation of the spatial location of every light source, localisation becomes possible using monocular cameras. One of the challenges we face is the gross change in light appearance as a function of distance due to flare, saturation and bleeding — city lights certainly do not appear as point features. To overcome this, we model the appearance of each light as a function of vehicle location, using this to inform our data-association decisions and to regularise the cost function which is used to infer vehicle pose. In this way we develop a place-dependent but stable sensor model which is customised for the particular environment in which we are operating. We demonstrate that our system is able to localise successfully at night over 12 km in situations where a traditional point feature based system fails.