Agreeing with Nhbenz... that "Aladdin-style" oil-lamp, with a flame coming out to show it is lit, giving light, represents "the Lamp Of Knowledge." That specific symbol has been frequently used in Academic/Scholarly emblems for centuries, particularly by schools & universities, not just Nursing.
Well-focused closeup photos of the maker's-mark on your pin's back may give us information which will help us identify it.
The specific form of pin-clasp on its back dates from the 1920s onward to the present.
So, as JonG indicated, the letters "S.U" on your pin are highly likely to stand for a University whose name starts with an S.