Psalm 90:8 Thou hast set our iniquities before thee, our secret sins in the light of thy countenance.

God's countenance refers to his face. And the light, which is the revelation, of his face (who he is) can be seen only in Jesus Christ.

Therefore, when when God's face was revealed (Jesus) our sin was set in "the light of his face". What does this mean? Consider:

Luke 8:17 For nothing is secret that will not be revealed, nor anything hidden that will not be known and come to light.

There is no sin ever committed or ever will be committed which was not brought "to light". It was all placed on his shoulders. But also consider this:

John 3:20 For everyone practicing evil hates the light and does not come to the light, lest his deeds should be exposed.

The exposure of our sin is not about God showing everyone how filthy we are, but its us coming before him, revealing ourselves to him who is already aware of our filthiness so he can clean us up.

Stepping into the Light (Jesus), exposes our sin (to God) so he can bury them forever in the Light (Rom 6:6) and thus we can Live forever in the Light.

Proverbs 16:15 *In the light* of the king's countenance *is life;* and his favour is as a cloud of the latter rain.