Ah, you are Down Under, so as your light is waning in autumn, as ours is increasing in spring here in the Northern Hemisphere. Decreasing daylength is the signal for the ducks to stop laying, while increasing daylength is the signal to start.
If you want to artificially add light to get them laying again, do so slowly, add about 1/2 hour to 45 minutes of light per light a week to the daylength they experience now until your ducks are getting 15 or so hours of light a day. I add light to the morning so that my ducks have already layed their eggs and are ready to go free ranging shortly after sunup. This may take a month or so to get them laying again, and they may go thru a molt because of the decrease in daylength they already experienced, but adding the artificial light gradually will get them all laying again.