You are referencing the words of our Lord in the Gospel of John. John 9:4-5 (NKJV), “I must work the works of Him who sent Me while it is day; the night is coming when no one can work. As long as I am in the world, I am the light of the world.”
The word light comes from Strongs Concordance G5457 – “phos” meaning to shine or to make manifest…”
Light in the context of our Lord’s declaration is truth and righteousness and the way to eternal life. John 14:6 (NKJV), “Jesus said to him, ‘I am the way, the truth, and the life. No one comes to the Father except through Me.’”
We are instructed by Jesus to let OUR light shine before men. Matthew 5:16 (KJV), “Let your light so shine before men, that they may see your good works, and glorify your Father which is in heaven.” For those trying to follow in the footsteps of Christ, we are to be representatives of that light by exhibiting true Christian attributes in our daily lives.
In the opposite direction, Satan represents the way to lies, darkness, and death. Darkness is often used in scripture to illustrate deceit and ignorance; for example – Isaiah 60:2 (KJV), “For, behold, the darkness shall cover the earth, and gross darkness the people: …” How well that describes the world we live in today where lies and ignorance are celebrated over truth and facts. Satan remains the god of this world. 2 Corinthians 4:4 (RSV), “…the god of this world has blinded the minds of the unbelievers, to keep them from seeing the light of the gospel of the glory of Christ, who is the likeness of God.”
Thankfully, Jesus is in the process of destroying the Prince of Darkness with the bright shining of His presence. 2 Thessalonians 2:8 (YLT), “and then shall be revealed the Lawless One (the man of sin), whom the Lord shall consume with the spirit of his mouth, and shall destroy with the manifestation (Greek means ‘shining’) of his presence”.
When God’s kingdom is fully established on the earth, when men have passed their final test and can then live forever, there will be no more darkness-sin and ignorance. Only eternal life-light will cover the entire earth.
Revelation 21:23-24 (ESV), “And the city (the New Jerusalem) has no need of sun or moon to shine on it, for the glory of God gives it light, and its lamp is the Lamb. By its light will the nations walk, and the kings of the earth will bring their glory into it,”