ESV - 12 Again Jesus spoke to them, saying, "I am the light of the world. Whoever follows me will not walk in darkness, but will have the light of life.
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Jesus said that at the feast of dedication or sometimes called the feast of lights. In the temple at the time would have been a huge menora that was lit durring the feast. The people would have understood the symbolism of the menora and Jesus saying ," I Am the Light."
Light illuminates the reality of things, and exposes things attempting to shroud themselves in darkness. Not only is Jesus the Truth, but He is the one who manifests this to whosoever will believe.