John 3:19-21 And this is the condemnation, that the light has come into the world, and men loved the darkness rather than the light, for their works were evil. For everyone who practices evil hates the light, and does not come to the light, lest his works be reproved. But he who does the truth comes to the light, that his works may be manifested that they wrought in God.
According to the context, truth here denotes uprightness (as opposed to evil — vv. 19-20), which is the reality manifested in a man who lives in God according to what He is, and which corresponds with the divine light, which is God, as the source of the truth, manifested in Christ. See note 6 in 1 John 1:6. (John 3:21, footnote 1, Recovery Version)