In Ezekiel 1, the brilliant light around the throne looked like what?

Answer: A rainbow in a cloud

The light around the figure on the throne was like a rainbow in a cloud on a rainy day: the likeness of the glory of the LORD.

“The appearance of the brilliant light all around Him was like that of a rainbow in a cloud on a rainy day. This was the appearance of the likeness of the glory of the LORD. And when I saw it, I fell facedown and heard a voice speaking.”— Ezekiel 1:28 (BSB)