The Orangerie Museum reopens to the public Friday after a painstaking six-year renovation, paying tribute to impressionists' love of light by installing a giant skylight and making the building again resemble a greenhouse -- its original use.

Workers tore up the low, drab ceiling that had sliced the museum horizontally, and a vast skylight now opens up above the impressionist masterpieces for the first time in more than four decades.

Tucked into the Tuileries Gardens, the stone structure once sheltered delicate orange trees in the winter before becoming home to Monet's mammoth water lily murals.

"The most important part of our work was to give the light back to the 'water lilies'," Olivier Brochet, one of the architects on the $31 million project, told The Associated Press as the museum was opened Tuesday for a preview.

"These paintings are so close to nature, weather and time that it was a crime to block out the sunlight," said Brochet, referring to a 1960 expansion that slapped a second story onto the museum, above the gallery housing "the lilies", depriving them of light.

On sunny days such as Tuesday, a new glass roof floods the water lily room with natural light; a freshly installed system of overhead spotlights will help illuminate the mammoth canvases on Paris' many cloudy days.

For the last three decades of Monet's life, his main subject was his front yard in the small French town of Giverny, with its lily-filled pond, Japanese bridge and weeping willows. He painted hundreds of works of water lilies and donated eight large-scale canvases to the French people at the end of World War I.