Maritime New Zealand is in the dark as to why the lighthouse at Nugget Point failed last week, but an investigation is under way.
The light was out for two nights, coming back online on Saturday.
Maritime New Zealand spokesman Steve Rendle said although there was an intense thunderstorm at Nugget Point at the time of the failure, it did not appear to be lightning-related.
The one or two outages a year in New Zealand's 142 lighthouses were normally lightning-related, but Mr Rendle said the lighthouse's rectifier had failed.
''There is no evidence of lightning,'' he said.
''But we're obviously having a look to see what happened there, because that's a pretty unusual occurrence.''
The failure of a lighthouse is so unusual the nearest equipment required to repair the Nugget Point lighthouse was stored at Christchurch, Mr Rendle said.
No issues were reported before the light was restored.
