In 1981, a supervisor asked him to change course once again. “He wanted someone who would not be caught up in daily work and could think about light,” Mr. Jousse said. “I knew a little bit about electricity, and I was an amateur photographer. So he invented a job for me.”

At the time, most of the Paris monuments were either unlighted or only crudely illuminated with big spotlights that shone directly onto the facades. Mr. Jousse sought out urban architects and theatrical lighting experts for ideas and technical training.

He eventually created a research laboratory for the city of Paris, where he and a team began to create fixtures and to experiment with the color and intensity of light. The city now spends about $260,000 a day on its lighting.

But that does not mean everything runs smoothly. The $2.1 million project to redesign the lighting of Notre-Dame — most recently the lighting of the south facade, which was inaugurated last week — has involved heartbreaking compromises.

For half a century, the only hint of light on the south facade came from spotlights on the far side of the Seine River. The new lighting scheme was intended to allow spectators to discover the cathedral’s facade slowly, through the power and drama of the details.

But as a national monument, Notre-Dame belongs to the French state, which has the right to veto any design decision. Stones could not be moved, walls could not be drilled. All material and equipment had to be moved in and out of Notre-Dame at night to avoid annoying tourists.

A bigger headache came from the Catholic clergy. The designers had planned to light the facade’s rose window from within, so that it could be seen in full color by passers-by. The priests called the idea sacrilegious.