Directed by Len Lye, 1936, 3:50
In true Experimental film style, Rainbow Dance lacks narrative and seems to be a continuous acid trip. It shows a dancer with various objects, and switches between scenes of this man and other shapes such as fish, and diagonal lines.
I think after a certain point, all experimental films contribute the same thing to the film industry, and to the film audience. Its main purpose is to give the audience a strange experience that they can't get from typical genres of film.
One element specifically prevalent in these experimental shorts is the lack of narrative. I think it's important to note that this is probably the main purpose of experimental films. They're the anarchists of the film industry. Rather than conform to the typical narratives that the rest of the genres follow, experimental films say, "Fuck that" and get their point across in their own way. This is important because it gives filmmakers a way to express themselves in a more abstract way.