Much of the dialogue is improvised.
Shot on 16mm with a skeleton crew of just four.
Marie Rivière first encountered Éric Rohmer's work in the early 1970s. She wrote a letter to the director, expressing an interest in working with him. This led to small parts in some of his films, culminating in this full collaboration with Rohmer where Riviere's contribution to the screenplay was so extensive, she received a co-writing credit. As such, the screenplay was actually just a framework for the actors as practically all the dialogue was improvised. Riviere would actually go on to make a documentary about Rohmer which she completed in 2010, just months before the director's death.
Note how Delphine - who is unwittingly in quest of the green ray - spends most of the film wearing red.