of a fragment that is lit by torchlight into a spectre

[suprunp]

Only their children’s had radiance, their eyes, the sheen on their hair, and in another way, their movements and their voices. Bright with a kind of unnatural brightness. It was not the wholesome lustre of a free flame, but of the hectic radiance that sheet-lightning gives suddenly to limbs of trees at midnight; of sudden flares in the darkness, of a fragment that is lit by torchlight into a spectre.
(M. Peake; Titus Groan)

Would you be so kind to 'translate' it?

Thanks.

[charliedeut]

You mean the part in bold?

To me, it conveys the image of something that is lit from behind (or of something which is between me and the point of origin of light) with a very intense (and very white, as the Xenon headlights in cars) beam. So strong that it seems to blur the edges of the figure, giving it a less bodily (or physical, if you will) aspect, more like a spectre.

That's just my reading, though. And from what I know, the text you're extracting from lately is rather... peculiar in its style, at the very least.