Your lamps must be connected to your bridge, to ensure that only you operate your lamps and not your neighbour’s (and vice versa). As long as the lamps are not yet connected to a bridge, they will flash briefly when you switch them on. To link lamps to your Bridge, have the App search the bridge for lamps, and then turn on the lamps one by one.
Each lamp flashes briefly when it is switched on, because it is then not yet connected. The lamp is usually found within 4 seconds and then flashes again to indicate that it is now connected.