WASHINGTON—The Trump administration is intervening to protect old-fashioned incandescent lightbulbs from rising energy-efficiency standards, a widely expected move that 16 states have already challenged, saying it undermines efforts to fight climate change.

The Energy Department is set to announce Friday that it won’t raise efficiency rules under a 2007 law it says would have effectively phased out the pear-shaped bulbs that were once ubiquitous in American households. Department officials say tightening those standards would…

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