Charles Ellicott Commentary Psalms 90:8

"Thou hast set our iniquities before thee, Our secret sins in the light of thy countenance." — Psalms 90:8 (ASV)

Our secret sins. —Or, to keep the singular of the original, our secret (character).

The expression, “light of God’s countenance,” usually means “favour.” But here the word rendered light is not the usual one employed in that expression, but rather means a body of light: “the sun (or eye) of Your countenance.” Compare:
“Then Seeva opened on the accursed one
His eye of anger.”
SOUTHEY: Curse of Kehama