by one's lights

Chiefly by the metaphor of lights as sources of illumination (e.g., lamps, lanterns, candles, torches) (thus, how something looks depends on the quality and quantity of the available light), but the sense of light as sightedness or vision is cognitively adjacent, setting up an interpretation of lights as referring to the eyes themselves (compare in my view); the potentially variable figurativeness behind punch someone's lights out is comparable here.

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by one's lights

1. (idiomatic) According to one's understanding.

   Synonyms: in one's eyes, in one's view, to one's mind, in one's opinion; see also Thesaurus:in my opinion

   • 2025 October 16, Ross Douthat, quoting Amy Coney Barrett, “Amy Coney Barrett Is Looking Beyond the Trump Era”, in The New York Times‎^[1], New York, N.Y.: The New York Times Company, →ISSN, →OCLC, archived from the original on 20 October 2025:

     Once you allow yourself and you open the door to letting outside pressures of any kind influence or dictate — especially dictate — your decisions, then it’s over. Therein lies madness. Because my oath requires fidelity to the Constitution and to decide these cases by my best lights.