Generally this is a control signal injected into the power to control/inform loads about the current rate (e.g.: peak, off-peak), and other tasks. Pulsadis is a common system in France for this.

Perhaps, however Pulsadis uses a 175 Hz carrier, and neither that nor the bit periods are anywhere close to the pulse frequency I've observed. The amplitude of the dimming does however seem to be consistent with that of the Pulsadis signal.