Candlelight is the soft, moving, yellowish light a burning candle gives. It is an uncountable noun, so you say 'by candlelight' or 'in the candlelight', never 'a candlelight' or 'three candlelights'. The most common shape by far is 'by candlelight': 'they ate by candlelight', 'people used to read by candlelight'. That little phrase does a lot of work — it can mean romance (dinner, a date), or it can mean poverty and the past (before electricity, before the power came back). Which one it means depends entirely on the rest of the sentence, so listen for the context. English also uses it in front of other nouns: a candlelight dinner, a candlelight vigil — that last one is a quiet gathering at night where people hold candles to remember the dead or to protest, and Taiwanese students will recognise it from the news. You may also see 'candlelit' (a candlelit room, a candlelit dinner); that is the adjective, and it is the more natural choice before a noun in British English. The word also carries a feeling that plain 'light' does not: gentle, warm, a bit unsteady, kind to faces. Writers use it when they want a scene to feel old, private, or tender.