What can we say about the light in the film?
Depends which context/scene you are referring to.
In the scene where Julia is standing behind the fence, looking at the train go by, the light (from the window) explicates the difficulty she has to endure - the light in the distance is seemingly unreachable and untouchable.. showing, to an extent, that it will be quite difficult for Julia to defy the odds and reach some sort of optimism in her life. The light also serves to highlight the contours of Julia's pain-inflicted face; so lighting is actually a really important technique in this film.
The 'very quick edits' are called vignettes - we are constantly drawn, as viewers, to see the journeys that all characters are enduring.. as a result of these vignettes, Sarah Watt doesn't allow any character's story to stand out from the crowd.