الْعِلْمُ نُورٌ.
Knowledge is light.
Both knowledge and light are named, while the comparative particle and stated ground are omitted. A standard classroom analysis treats this as an eloquent simile: the two sides are expressed and the shared quality is illumination or guidance.
Calling every figurative identification an istiʿārah is imprecise. A metaphor typically transfers an expression from one side to the other; the explicit presence of both sides makes tashbīh balīgh the more straightforward analysis here.