What does the age of seven bright and nine dark mean?

Dark Nine: à n ji incarnation, a Chinese word. In ancient times, "nine" was the highest positive number, so every nine was a difficult period. Eighteen, twenty-seven, especially fifty-four, sixty-three and seventy-two, such multiples of nine are called "dark nine".

Qi Ming: Commonly known as "Qi Ming" means: seven, seventeen, twenty-seven and thirty-seven.

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In ancient times, "Nine" was the sunshine, so every nine days was a difficult time, such as nine, nineteen, forty-nine and so on. This is called "Ming Jiu", and a banquet is usually held to invite guests to pray for disaster relief.

Eighteen, twenty-seven, especially fifty-four, sixty-three and seventy-two, such multiples of nine are called "dark nine". Although they don't entertain guests with big banquets, they usually go to the temple to pray for disaster relief. This tradition still exists in some places.

The eighty-eighth story of A Dream of Red Mansions: Yuanyang said, "The old lady is going to write 36,501 Diamond Sutra, because she will be eighty-one years old next year. She is a dark nine and has made a promise for nine days and nights."

Baidu Encyclopedia-Dark Nine