حَصَلَ فِي قَلْبِي نُورٌ
A light arose in my heart.
If the context concerns gaining knowledge or understanding, the expression depicts inward comprehension through the sensory image of light. An abstract intellectual state becomes vivid and immediate.
By contrast, “knowledge is like light” openly declares resemblance. The two formulations differ in structure and force: the first pictures light arising in the heart, while the second merely compares knowledge to light.