Absolute brightness was absolute darkness. That was a simple fact many people understood. Prince Long Qing was inspired by this in the Headmaster's illusion test when he competed with Ning Que. As the owner of the illusion, how could the Headmaster not understand? Just like he felt: the great Way makes everything the most simple.
Ning Que had read the "Ming" Handscroll and Buddha's notes. He and Sangsang had been considered as the Son and Daughter of Yama when they were in the Desolate Man's tribe. He had a deep understanding of the related knowledge of Yama. Hearing his teacher and recalling the books he had read, he worked out the problems that had bothered him for a long time.
The Desolate Man's tribe called Yama Lord Guang Ming in the ceremony, who was the Lord of Light. There were many records about the Unmovable King also in the notes of the Buddhism Sect and that should be the Invariant Yama.
"Ming" was the Light.
The Lord of Light was Yama.