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light (up)on someone or something
1. Lit. to land on someone or something; to settle on someone or something. (Upon is formal and less commonly used than on.) Three butterflies lit on the baby, causing her to shriek with delight. The bees lit on the clover blossom and pulled it to the ground. Her glance lit upon a dress in the store window.
2. Fig. to arrive at something by chance; to happen upon something. The committee lit upon a solution that pleased almost everyone. We just happened to light upon this idea as we were talking to each other.
Also, light upon. Happen upon, come across, discover. For example, John was delighted to light on a new solution to the problem, or We were following the path when suddenly we lit upon a cave. [Second half of 1400s]