Obviously the flame can stand further in symbolism when characterizing the life we perceive in that it is but an artificial attempt to replicate the sun, which shines so bright that it "blinds" the liberated prisoner.
The flame however fails to do this. However, along with saying that this further attributes to the stark contrast between the flame, false reality, and the sun, truth itself, I can also intertwine the idea of perfect forms as well.
Recall from class that the derivative form of any truth is but a replication of the real thing and is therefore less powerful in its existence.
I believe we could say that the flame is a derivative form of the sun, which is, if not scientifically, definately symbolically is the perfect form of light, which allows us to see.
From there one can generalize this to truth all together, a symbol light sometimes, and in this case does stand for.
So to conclude, we could determine that because the flame is a derivative form of the sun, it can reasonably contribute to the perception of life within the cave, which is only comprehended through the five senses.
I guess I could also go back to how the sun blinded the liberated prisoner when he saw it, perhaps suggesting that this new light rejected his old means to understand something.
Well, I guess that's about it.