"Please turn off the lights" is how you would say "请关灯" in English. The phrase comes from the verb "to turn off," which means to cause something (in this case, the lights) to stop functioning or operating. Here are some example sentences using this phrase:

Can you please turn off the lights when you leave the room?

I always forget to turn off the lights in the basement, so I'm trying to be more conscious of it.

I'm trying to save energy, so I've been turning off the lights more often in my house.

In Chinese, these sentences would be translated as follows:

离开房间时，你能请关灯吗？

我总是忘记关地下室的灯，所以我正在努力注意它。

我正在努力节约能源，所以我最近在家里经常关灯。