lights in communal area

The lights in the communal area of my building have stopped working. It is the normal system whereby they are on for 30 secs or so after you push one of the switches. I thought that I would try this forum before calling electrician, in case it is simple to fix. I checked the trip switch in basement and it is ok. Does anyone have any ideas? One time they stopped working because someone had put a high wattage lightbulb in one of the sockets, but this is not the case this time.