刘老师从构词的角度作了分析，下面从两词用法的角度作一区分：
▲darkened 主要用于说明室内没有光亮（尤其指没有灯光）。《柯林斯高级英语学习词典》对 darkened 的解释是 A darkened building or room has no lights on inside it.《麦克米兰英语词典》对 darkened 的解释是 a darkened room or building is dark because there are no lights on inside. 如：

(1) His cigar glowed in the darkened room. 他的雪茄在黑暗的房间里闪着火光。
(2) I felt my way through the darkened room. 我在这间黑暗的房间里摸索出去的路。

(3) The fans sat enthralled in the darkened cinema. 影迷们坐在黑漆漆的电影院里看得如痴如醉。
(4) The building was darkened except for a single light burning in a third-story window. 整座大楼一片漆黑，只有3层的一个窗户透出一丝光亮。
▲dark 的用法则比较广，可用于室内也可用于室外，可指没有灯光也可指没有光线（自然光）。如：
(1) It’s too dark to see clearly. 太黑了看不清。
(2) It was dark because the light had gone out. 很黑，因为电灯熄灭了。
(3) She made her escape in a dark night. 她在一个漆黑的夜晚逃走了。
(4) It grew dark before we finished our work. 我们还没有干完活天就黑了。
(5) It was so dark that he couldn’t see anything. 天是那样黑，他什么也看不见。
(6) She avoids walking on dark streets at night. 她避免夜间在黑暗的街道上走路。
(7) His eyes focused slowly in the dark room. 他在那间黑屋子里眼睛慢慢地看清了东西。