You mentioned that light is, or can be, a metaphor of moral qualities, namely holiness and purity. Could you please show how it is used as such a metaphor in Scripture?

This text is from a transcript of a talk by David Gooding, entitled ‘Unity, Origin and Victory’ (1987).

Well, I was suggesting that light, in the first place, has to do with things intellectual and of the mind—God's self-revealing of himself intellectually. The opposite of darkness, of ignorance and falsity: it is truth. But I suggest it is a matter of moral purity, not just intellectual. If you want a citation of a verse that seems to say that, Isaiah 5:20, for instance, seems to me to be using the metaphor in that sense: 'Woe unto them that call evil good'. So now we're in the realm of things moral—'that call evil good and good evil'—and then illustrating it he adds, 'that put darkness for light, and light for darkness', and then illustrating it again, 'that put bitter for sweet, and sweet for bitter!'

Here then, the words 'light' and 'darkness' are used in a moral context: 'light' standing for what is good, 'darkness' standing for what is evil, and God complains that the people confound the two. In the New Testament, it seems to me, its usage indicates that it's not merely a matter of truth, but also of moral quality. John 3:19–21 is the passage I would quote: 'Everybody that doeth good cometh to the light that his deeds may be made evident that they are wrought in God. Everybody that doeth evil, he doesn't come to the light, he hates the light, because his works are evil'. And though there is the idea of exposure, what it's exposing is moral evil, or moral worth.