light dawns (on one)

Something suddenly becomes clear, certain, or fully understandable to one. The light dawned when I remembered that my grandfather had been stationed in Japan many years ago. It wasn't until I was able to say it out loud that the light dawned on me about what really happened.

(the) light ˈdawned (on somebody)

somebody suddenly understood or began to understand something: I puzzled over the problem for ages before the light suddenly dawned on me.

light dawned, the

At last one understands; one finally grasps the meaning or an idea, or the like. Strictly speaking this expression is tautological, since the noun dawn means the reappearance of light and the verb to dawn means to become light. However, when it is transferred to human perception, as it has been since about 1800, it makes sense as the beginning (dawn) of understanding (light). The British locution does not raise this problem, since it is came the dawn.