“明暗界限”可以翻译为 "boundary between light and shadow" 或 "demarcation line between light and dark"。
"boundary between light and shadow" 更侧重于描述明暗之间的分界线，常用于艺术、摄影或光学领域。
"demarcation line between light and dark" 强调了分界线的明确性，适用于需要精确描述的场景。
根据具体语境，可以选择更合适的表达。