PORTLAND, Maine — The Maine Supreme Judicial Court on Tuesday vacated a decision by the Maine Department of Environmental Protection over nighttime sound requirements for the Saddleback Ridge Wind Project in Carthage, Canton and Dixfield.

The court unanimously agreed with the groups’ appeal of a ruling by the Board of Environmental Protection that backed the DEP’s decision that the nighttime noise level for the windmills should be at or below 45 decibels. Writing for the court, Justice Warren Silver said the nighttime decibel level should be 42 or below.

While the project’s application was pending before the DEP, the agency recommended to the Legislature that for the health and safety of those living near wind farms, the acceptable nighttime decibel level should be lowered from 45 to 42, the opinion said. The DEP set the nighttime noise level for the Saddleback project at 45 decibels five months before the Legislature approved its recommendation that the acceptable nighttime level be lowered to 42 decibels.

At the time the DEP approved Saddleback’s application on Oct. 6, 2011, the standard for nighttime noise levels was 45 decibels.

The new law requiring the lower level went into effect June 19, 2012.

The justices heard oral arguments in the case when they convened in Bangor on Nov. 8, 2012.