This is a very simple, enclosed-lamp fixture. The light bulb is protected from contact with the outside world. This type of fixture has become mandatory for clothes closets where a surface mounted fixture is installed. This is to prevent people from stacking up clothes, blankets, or boxes right up to the bare bulb and starting a fire. Apparently, that happened enough to cause them to change the code. (They will also permit a recessed light or a flat florescent fixture) So if you live in one of the thousands of apartments in Chicago where you have the bare bulb and pull string controlling it in the closet, it is illegal.
Bet ya never knew!