What do you mean, only the Duke of Zhou can set fire and the people are not allowed to light lamps?

Only state officials are allowed to set fires, but people are not allowed to light lamps. This means that officials are allowed to set fires and people are not allowed to light lamps. It means that powerful people can run amok by themselves, but even the legitimate activities of the people are restricted.

From Lu You's Notes on the Old Learning Temple in Song Dynasty, Volume 5:

Tian Deng is a county magistrate. He keeps his name secret. Anyone who touches him will be angry, and many officials and soldiers are condemned by the list. So for the country, the light is fire. In the Yuan Dynasty, people were allowed to visit our state. The official then revealed the list of books in the city and said, "The state set it on fire for three days according to law." Therefore, as the saying goes, "only state officials are allowed to set fires, and people are not allowed to light lamps." Stupid.

Translation:

He used to avoid using his own name when he was a state official. Anyone who makes a mistake in his name will be angry, and most officials and soldiers will be punished for it. So people have to call it "fire lamp". On the fifteenth day of the first month, lanterns were decorated to let the people go into the city to watch. Officials wrote a notice and announced it in the market: "As usual, the state government set fire for three days." So he said, "Only state officials are allowed to set fires, and people are not allowed to light lamps." This is where it came from.

Extended data:

When Tian Deng became the prefect, he was afraid that others would say or write his name, so the people in Quanzhou had to read or write the word "light" as "fire".

On the Lantern Festival, the state will put on three lanterns for the common people to see. Because the officials were afraid to read and write the word "light", which violated the taboo of the celestial prefect, they wrote a notice and posted it on the market, saying, "The state government set fire for three days as usual."

This idiom story comes from Notes of Old Xuegong. Lu You, a famous poet in the Southern Song Dynasty, wrote Notes on the Old Learning Temple, mainly recording anecdotes and textual research, and occasionally using folklore.

Taishou Tian Deng, fish the people, is overbearing, so that the people are not allowed to say the word "Deng" and write the word "Deng" and the word with the same sound as "Deng". Otherwise, it is disrespectful to him, ranging from being beaten to being executed. Therefore, on the third day of the last Lantern Festival, the "An Min Notice" had to be rewritten as "Set fire to it for three days", which caused an ironic joke.

The idiom "only state officials are allowed to set fires, and people are not allowed to light lamps" is summed up from this story. Now people use it as a metaphor for a reactionary ruler who is autocratic and barbaric and can do bad things at will, but the legitimate behavior of the people is restricted by various kinds.