Jesus is also the true Light because He does not merely give light; He is Light. He is the Light of life (John 8:12). He stands in contrast to the darkness of sin that has infiltrated the world and contaminated everything in it.
He who loves his brother abides in the light (1 John 2:10, NKJV).
What is “true” light? John refers to the new commandment in respect to the true Light. “Again, a new commandment I write to you, which thing is true in Him and in you, because the darkness is passing away, and the true light is already shining” (1 John 2:8).
Isn’t light, light? There may be different intensities of light but how is light “true”? Again, the answer is Jesus. Just like the old commandment to love one another is new in Him, so He is the true Light that was to come into the world.
John highlights Jesus as the true Light in the prologue to his Gospel. Speaking of Jesus as the eternal Word of God, incarnate to give life, John says, “That was the true Light which gives light to every man coming into the world” (John 1:9). This light is not overcome by darkness but rather overcomes it.
In one sense, Jesus is the true Light in contrast to the shadow of the Old Testament.