adverb, adverb taking the 'to' particle
brightly lit; lit up
Describes a space or object that is brightly illuminated, often with a warm or vivid light. Commonly used with と as an adverb.
部屋の中は明々と輝いていた。
The room was brightly lit.
月明かりで庭が明々と照らされた。
The garden was lit up by the moonlight.
明るい is the common adjective for 'bright' or 'well-lit'; 明々 is a more literary adverb emphasizing vivid illumination.
煌々 also means 'brightly lit' but often implies a dazzling or glaring light, while 明々 suggests a softer, warm brightness.
Reduplication of 明 (あか, 'bright') with the iteration mark 々, forming an adverb meaning 'brightly'. The exact historical derivation is uncertain, but it follows a common pattern for mimetic or emphatic adverbs.