The fourth feature from Tisch professor Ira Sachs, “Keep the Lights On,” chronicles the destructive relationship of documentary filmmaker Erik, played by Thure Lindhardt, and closeted lawyer Paul, performed by Zachary Booth. What begins as a random hookup evolves into a romantic partnership put at risk by Paul’s drug addiction and Erik’s need for secrecy, leaving the couple shrouded in the darkness of their shame.

Sachs and co-writer Mauricio Zacharias sorted through emails, letters and various memorabilia that chronicled Sachs’s own decade-long relationship that served as inspiration for the film.

“I’m interested in a sort of personal filmmaking, which brings a lot of one’s experience into the creation of a film,” Sachs said.

But “Lights” is far from a literal adaptation of Sachs’s own life. Though the words remained the same from scene to scene, and the characters’ actions were already set, Sachs’s particular style of directing provided plenty of room for improvisation. Developing the characters meant keeping the emotional reactions fresh. Spontaneous reactions set the scene and vary from one moment to the next. Sachs is comfortable referring to his work as a piece of documentary filmmaking because the actors’ emotions in these moments were to never occur again — preserved only on film.

“There is no repetition of emotion,” Sachs said.

Lindhardt, a Danish actor best known to American audiences for his role in “Into the Wild” and “Angels and Demons,” is good friends with Booth, best known for his role on “Damages.” The friendship between the two actors added comfort and a sexual chemistry to the film, as the actors were exposed physically and emotionally.

The actors and the crew needed to feel content with expressing themselves, both on and off camera. Sachs served as the manager of this atmosphere. An inquisitive director, he was as interested in the actors and their personal lives as he was with the final product of his film.

Layered over the emotionally involved plot is the film’s inspirational score, composed by musician Arthur Russell, who passed away from AIDS in 1992.

“[His music] has a depth, messiness, beauty, melody and a certain kind of timelessness,” Sachs said.

Russell’s personal story as a gay man is reflected in his music, which in turn adds emotional complexity to the film. Every aspect of “Keep the Lights On” — the directing, acting, writing, music and even the real lives of the film’s creators — is bursting with feeling.

A version of this article appeared in the Sept. 6 print edition. Erika Zelis is a contributing writer. Email her at [email protected].

In the previous version of this article, WSN incorrectly reported that Lindhardt and Booth are actors in “Damages.” In fact, only Booth is an actor on “Damages.” WSN regrets the error.