During the war, there were several hours of blackouts every night.

blackouts 是名词 blackout 的复数形式。blackout 由 black（黑色的）和 out（完全、彻底）组成，字面意思是"完全变黑"，引申为"灯火管制"，指为防止敌方发现目标而强制熄灭所有灯光的措施。