Symbols are objects, characters, figures, or colors used to represent abstract ideas or concepts.

Lightning

The speaker references lightning in the second stanza, where they discuss the reason “wise men” resist death. In this context, lightning symbolizes a flash of insight or inspiration. The stanza (lines 4–6) reads as follows:

     Though wise men at their end know dark is right,
     Because their words had forked no lightning they
     Do not go gentle into that good night.

Wise men are wise precisely because they understand that death is a natural part of life. Even so, they refuse to “go gentle into that good night” because they’ve not yet achieved something they wanted to achieve. We could read the phrase “their words had forked no lightning” in multiple ways, but one possible interpretation is that these wise men never managed to produce work that made an impact on the world. That is, they haven’t yet found a way to inspire others with their words (poetry perhaps?), and they want to stay long enough to do so. In this case, the lightning represents the flash of insight that’s necessary to inspire others. Since the “wise men” referenced by the speaker have not yet been able to pass their hard-earned wisdom, they feel a need to resist the temptation of death’s final rest.

“Green bay”

In the third stanza (lines 7–9), the speaker references a mysterious “green bay”:

     Good men, the last wave by, crying how bright
     Their frail deeds might have danced in a green bay,
     Rage, rage against the dying of the light.

The basic sense of these lines might be paraphrased as follows: “good men” (line 7) rage against death because, even though they have done many good deeds, when they look back on their life, they regret not having done more. The good men referenced by the speaker find themselves nearing the end of life. If we imagine life as a beach, the “last wave” would have just passed them by. This wave symbolizes the last meaningful opportunity for good men to live fully and do good deeds. Once this wave has passed, and as the men look back on their lives, it’s hard for them not to feel inadequate. Despite their best intentions, their deeds were all “frail” and failed to do as much good as they’d hoped. From this vantage, these men imagine some “green bay” where their deeds “might have danced” more vibrantly. With this reading in mind, the green bay may symbolize the vitality of youth. But it also—and more importantly—symbolizes the possibility of final fulfillment. It’s precisely out of a longing to achieve such fulfillment that “good men” rage against death.

Meteors

The speaker references meteors in the fifth stanza (lines 13–15), which concerns the way “grave men” defy death:

     Grave men, near death, who see with blinding sight
     Blind eyes could blaze like meteors and be gay,
     Rage, rage against the dying of the light.

In these lines, the speaker focuses on “grave men.” This is a punning phrase that turns on the double meaning of grave, which is both an adjective that means “solemn” and a noun that refers to a burial site. Men who approach the grave with excessive solemnity may realize, with a flash of insight, that they could still find a sense of happiness and contentment. The image Thomas uses to express this idea is complicated and dense, but on a basic level it plays with a tension between vision and blindness. The grave man has a solemn vision of death, but this vision effectively blinds him to the possibility of happiness. Any moment, though, he could have a flash of insight so illuminating that, like the blaze of meteors, it could produce a “blinding sight.” Such a blinding sight might replace his solemn vision of death and with the realization that his eyes, though “blind,” could still “blaze like meteors and be gay.” Understood in this way, the meteors symbolize both the source of insight and the insight itself.