What made Lights of New York the first all-talking feature film?

The Lights of New York (1928) is recognized as the first "100-percent talkie" feature film because it was the first full-length motion picture to feature synchronized spoken dialogue throughout its entire runtime.12

While earlier films like The Jazz Singer (1927) are often associated with the transition to sound, they were essentially silent films that utilized the Vitaphone system primarily for musical scores and sporadic, limited episodes of synchronized singing or speech. In contrast, the majority of the dialogue in The Jazz Singer was still delivered via the traditional written intertitles characteristic of the silent film era. The Lights of New York marked a significant technological and stylistic shift by abandoning these intertitles in favor of continuous, synchronized dialogue, setting a new standard for the industry.12