This indicates normal operation and when the cell is working and if TDS levels are within range the dot will remain on at all times whilst in operation in the FIRST TIMER.
If the dot is switching off and on, this indicates TDS levels are slightly higher than recommended and the unit will self-regulate to ensure that 15g/hr of chlorine is constantly produced and therefore not increasing chlorine levels in the pool.
The longer the dot is off the higher the TDS levels in the pool and the shorter the dot is off the closer to the recommended levels, which is normal operation.