回复30楼:这个是美国生活常识了
Why do stores keep the lights on at night?
For security and advertising.
Lights on deter thieves.
It makes security cameras work better
It allows passing security patrols (private and police) able to see activity inside that shouldn't be there.
the lit up store is inviting with window displays and advertising visible to passers-by

这解释不全面，因为全面的解释包含了不好的原因
万一要是没开灯，某个路人摔了，律师能告到的赔偿金，够你一直开灯很多很多年
美国的律师也是一特色