One specific scene which stands out is the interview with the homeless woman. She speaks of the loss of her children in a fire while she was in jail. The interview is of a mid-shot with low-key lighting. Only half of her face is viewable, the other side remains in the darkness. Her distress and sorrow is evident and the darkness adds to the effect of her grief. A sympathetic viewer is then brought back from a black out to the image of her smoking from a crack pipe. There are various extreme close-ups on the pipe, her inhaling, puffing it out and getting high, trying to balance out her lows.
It clear this is a dark time in her life. Consistently throughout the film, through the use of lighting, close-ups on crack, rats, garbage which they call food and the black and white film, we see just how black and white these peoples lives are truly. Singer successfully portrays this from the beginning until the end of the picture.
http://www.youtube.com/watch?v=wfxg6OQq0jE&feature=related