'Let the Sunshine In' shows radiance ofJuliette Binoche

In the first scene of “Let the Sunshine In,” Isabelle, a Parisian artist, is in bed with one of her lovers, a portly, ginger-bearded banker named Vincent.

He is quite impressed with his amatory skills, which makes one of them. The scene - tender, awkward, comical - is candid but not graphic, the vibe less voyeuristic than analytical.

What people say and do while they're having sex is revealing, not only of their bodies but also of their feelings, egos and motivations. So if we want to know who Isabelle is and what she's like - the principal concern of Claire Denis's shrewd and uncompromising new film - then the bedroom might be as good a place as any to start.

Denis, consistently the most interesting French filmmaker of the 21st century (see “Beau Travail,” “White Material” and “35 Shots of Rum,” among others), focuses her attention on a subject that could easily have been rendered sad, sensational or sentimental.

The sexuality of middle-aged women, when it comes up at all in Hollywood, tends to be treated with either pity or condescending encouragement.

As played by Juliette Binoche, Isabelle is defiantly immune to both of those, and even, at times, to the audience's sympathy. Binoche, effortlessly charismatic and ruthlessly unvain, has no investment in the character's likability.

She and Denis could not care less what you think of her. “Let the Sunshine In” commits itself to taking Isabelle on her own terms.

The challenge, for her and for the audience, is to figure out what those terms are.

This has a lot to do with her relations with men, sexual and otherwise.

The film is partly an impressionistic chronicle, by turns comical and melodramatic, of her affairs - the French word is histoires - with various unsatisfactory men. In addition to Vincent (Xavier Beauvois), who is married and intends to stay that way, there is a moody unnamed actor (Nicolas Duvauchelle) who uses ambivalence as a kind of foreplay, and François (Laurent Grévill), Isabelle's ex-husband and the father of her briefly glimpsed 10-year-old daughter.

Later, on a trip to a provincial art festival, Isabelle meets Sylvain (Paul Blain), whose working-class background dismays one of her snooty art-world guy friends, who no doubt thinks Isabelle would be happier with him.

But Isabelle suspects she might be happiest with Marc (Alex Descas), who gently defers (but doesn't entirely decline) her advances.

Happiness is elusive, and to some degree irrelevant. Isabelle is fascinating - puzzling, charming, irritating, worth caring about - because she's intelligent and free.

The shape of the film, which ambles through her days and nights in a way that feels more causal than it is, reflects the elusive pattern of her experience. She is impulsive rather than systematic, but nonetheless serious in her desire to figure out what she wants.

Toward the end, she turns for help to a spiritualist of some kind, a healer whose arrival is a dazzling and confounding surprise. I don't really believe in spoilers, but to name the actor who plays this man would be a betrayal of France, cinema and everything else I hold dear. (Resist the urge to Google.)

He counsels Isabelle to develop an “interior sun,” a phrase that supplies the film's French title and that is bizarrely reversed by the English translation, which irrelevantly evokes “Hair.” (“I would never have chosen that title,” Denis said in a recent interview in The Guardian.)

Even though Isabelle is counseled to remain “open” (her adviser uses the English word), Denis makes it clear that external sources of illumination are as untrustworthy as men. Binoche is the film's primary and sufficient source of light. The radiance is all hers. The clouds, too.