When Jack Paar left the “Tonight” show in 1962, he passed through a set of curtains and the camera zoomed in on a card that read: “No More to Come.” Three decades later, Johnny Carson had Bette Midler serenade him on his penultimate show, then sat and spoke directly to his fans in his emotional finale, watched by 42 million viewers.

But as Jay Leno, who is 63, exits the “Tonight” stage for the last time Thursday night, making way for the 39-year-old Jimmy Fallon to step in, the occasion has been marked by a notably less sentimental celebration of his tenure.

Any changeover behind the desk of the 60-year-old “Tonight” show represents a cultural pivot point. Mr. Leno’s departure after 22 years, almost all of them at the top of the ratings, is a generational shift that includes a geographic shift as well: a host young enough to be Mr. Leno’s son is his successor, and “Tonight,” the pioneer of late-night television, is returning to its roots, moving from Los Angeles back to New York.

Despite the diminished state of late-night television, and technology that has altered viewing habits, Mr. Leno’s show remains one of the signature franchises of broadcasting and still carries unusual resonance.