He is the radiance of the glory of God.
The word ‘radiance’ literally means to send forth light.  And with Jesus saying in John 8:12 that he is the “light of the world.  Whoever believes in me will not walk in darkness, but have the light of life,” we know that his light radiates from God the Father. 

Warren Wiersbe noted,

“Christ is to the Father what the rays of the sun are to the sun.  He is the radiance of God’s glory.  As it is impossible to separate the rays from the sun, it is also impossible to separate Christ’s glory from the nature of God.”

Do you see what this is?  No, the sun and the rays are not the same thing, but think about this: if the sun’s rays in our solar system did not eminate from the sun, would we see the sun? 

John 1:9-14 perfectly sums this up:

9 The true light, which gives light to everyone, was coming into the world. 10 He was in the world, and the world was made through him, yet the world did not know him. 11 He came to his own, but his own did not receive him.12 But to all who did receive him, who believed in his name, he gave the right to become children of God, 13 who were born, not of blood nor of the will of the flesh nor of the will of man, but of God.
14 And the Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth.

You see, those outside of Christ are blinded to His light. They cannot see, even though they believe they see more clearly than anyone else.  It’s takes eight minutes and nineteen seconds for the sun’s light to make it the 93 million mile trip to earth.  But while God had sent prophets before that simply reflected His light, only the Son radiated it!  And though he was in the world, the world (nor even the Jews who expected him the most) never ‘saw’ him.  And those who were born again have eyes to see… and when we see Jesus, we see the Father. 

Have you seen His light?  Second Corinthians 4:4-6 says,

“4 In their case 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 image of God. 5 For what we proclaim is not ourselves, but Jesus Christ as Lord, with ourselves as your servants for Jesus’ sake. 6 For God, who said, “Let light shine out of darkness,” has shone in our hearts to give the light of the knowledge of the glory of God in the face of Jesus Christ.

John Piper was right: “Seeing and savoring this glory is the spring of all endless joy.”