Taxpayers spent close to $15,000 to turn the Sydney Opera House green to promote the 2016 census, without any clear reference to the national survey.

Key points: Internal documents show green lighting cost $14,850 for setup, equipment hire, management and support

Internal documents show green lighting cost $14,850 for setup, equipment hire, management and support ABS chief statistician described green lights as a "major public relations opportunity"

ABS chief statistician described green lights as a "major public relations opportunity" Several sites around Australia went green to promote the census

The seven sails of the national landmark were lit up for two nights but did not include any information about the census, the website, a hashtag or branding.

Internal documents show the bureau of statistics spent $14,850 for set-up, equipment hire, management and support.

The Australian Bureau of Statistics (ABS) chief statistician David Kalisch described it as a "major public relations opportunity" and said it was likely to attract "social media influencers".

"This will maximise awareness and engagement with the census, and help create a national conversation," Mr Kalisch wrote in the document.

The Opera House turned green for census night and the night before but the social media conversation was dominated by the website's failure.

There was a 40-hour outage caused by four Distributed Denial of Service (DDoS) attacks that had been the subject of a blame game between the Australian Bureau of Statistics (ABS) and contractors for months.

The Opera House was part of a national campaign to light up landmarks with the colour green.

The Melbourne Arts Centre, Canberra's Telstra Tower, Brisbane's City Hall and the Darwin Convention Centre were some of the 20 sites to "go green" for the census.

At the time, the head of the census Duncan Young said it was a "magnificent way to mark the occasion".

"The colour green was chosen to represent the 2016 census as it reinforces this year's digital and environmentally friendly approach," he said in a statement.

The Bureau of Statistics was pushing Australians to fill out the form online instead of a paper version to be more environmentally friendly and save money.

The total census campaign media budget was $12 million.

The Government has reached a confidential settlement with computer giant IBM for costs over the system outage.

Editor's note (23/12/16): This story has been updated to make clear the cost of lighting up the Opera House was $14,850, not the $192,000 the Bureau of Statistics originally planned to spend.