By Day By Night is a Mexican science fiction movie where the over-population problem has been solved by programming people to operate in either day or night, and not both. This means that the population are only conscious half the day and the day people can never interact with the night people. This is a very meditative sci-fi film. It deals with concepts as opposed to thrills, action and suspense. It is beautifully photographed, has a nice ambient soundtrack and it does have a poetic final scene on a beach. However, it is perhaps a little too ponderous for its own good and moves quite slowly. I don't want to be too negative though, as it's good that the film-makers have tried to make something quite thoughtful here. Although it can only be recommended to people who are interested in the slower and more conceptual side of the genre.