意思：灯灭了；灯都关着；没有灯光

这里 out 不是“出去”，而是表示灯光熄灭/不亮。

句子结构

the lights = 灯
were = be 的过去式
out = 熄灭的、不亮的

所以：

The lights were out.
灯灭了。 / 灯都关着。

例句

When they arrived, the lights were out.
当他们到达时，灯已经灭了。

The lights were out in the compound.
那个建筑群里的灯都是关着的。

⭐ 注意两个很容易混淆的表达

The lights were out.
= 灯灭了 / 没有灯光

The lights went out.
= 灯熄灭了（强调“从亮到灭”的动作）

例如：

Suddenly, the lights went out.
突然，灯灭了。

所以 were out 更强调状态，went out 更强调发生了熄灭这个动作。