There are lots of figures of speech in the second stanza of "Anthem for Doomed Youth," most of which draw on a motif of light and darkness. For example, in the opening line, "What candles may be held to speed them all?", the "candles" are symbolic of remembrance. The rhetorical question implies that these soldiers will not be remembered adequately for their sacrifices.
In the next line, the speaker says that "in their eyes / Shall shine the holy glimmers of good-byes." The light in the eyes of the soldiers here might be symbolic of the hope with which they set out for war. The fact that the light only "glimmers" suggests that it is a weak, faint hope. The adjective "holy" to describe the "glimmers" of light alludes to the purity and innocence of the boys setting out for war.
In the following line, the speaker says that "the pallor of girls' brows shall be their pall." A pall is a piece of cloth draped over a coffin at a funeral. The metaphor describing the "pallor of girls' brows" as the soldiers' pall implies the deaths of the soldiers will be marked by the sickness of the girls they leave behind.
The concluding line of the poem, "And each slow dusk a drawing-down of blinds," uses symbolism and imagery to emphasize the number of deaths consequent of war. The dusk is a time of the day when light is fading to be replaced by darkness. Dusk is thus usually symbolic of death or dying. This image of darkness is then compounded by the image of the "drawing-down of blinds." The impression of darkness alludes to the lives of the soldiers being extinguished. And these deaths are as inevitable as is the setting of the sun.