Optical fibers are made of either glass or plastic and usually are not much thicker than a coarse human hair. Their small diameter makes them quite flexible. They are designed to function as a wave guide or a "Light Pipe" to transmit light from one end to the other with very little loss. These fibers are typically used in fiber-optic communications where light is used to transmit data (sound, images, text, etc.) over very long distances. Most of the time several strands of optical fiber are bundled together into a fiber-optic cable.
Humans are much like a single strand of a fiber-optic cable. Like the optical fiber, our existence is meaningless unless we are conducting light. And like the optical fiber, none of us have any light of our own and can only transmit whatever light we are near.
There is only one Source of Light (Jesus, John 1:9), so when a human gets close to this Source he/she begins to glow, just like a fiber-optic strand glows when it is near light. Neither an optical fiber, nor people, have to work at transmitting light. It just comes naturally.
Again, all fiber-optic strands that are facing the light will transmit that light. The closer they are to the light the brighter they are and so it is with Christians. Jesus said that people are known by their fruits. In other words, it's what Christians transmit that sets them apart; it's Who they are close to that makes the difference. If something comes between a Christian and the Light, then "his" light goes out or dims. Christians are known by "their" light.
Many Christians believe in the Trinity of God. Three in One. Think of Them as the Source of Light, but each One having a little different function or even personality so that a different "color" of light is created.
Each Christian may reflect a totally different "color" because God is much more than any one of us can show the world. Someone looking at a specific Christian will only see what that Christian sees in God, but as long as each Christian stays close to God he will display exactly what God is like. (Our God is so amazing and so full of surprises that as we look at each other we might see something totally different than WE have been seeing. But instead of criticizing others for not looking like us and believing like us, we need to keep our eyes on Jesus and not worry about the color someone else is displaying. Remember, God is the only Source of Light, so if you see light reflected in someone else then it is His light, no matter what "color" it is.)
Most optical fibers are called "end glow" because light is suppose to come out of the end and not the sides. If an "end-glow" fiber allows light to escape from the sides it is because it has been damaged. When Christians are "damaged" by hardship, pain and suffering the Light inside can be seen from all sides as well because each "damage" allows the light within (God's Light) to escape through their damaged lives. Now the Light comes out in other directions, and God's glory can be seen even easier than before. (PRAISE God for allowing you to be damaged. Now He can use you in ways you had never dreamed of.)
Jesus spoke to the people once more and said, “I am the light of the world. [the Source of your Light] If you follow me, you won’t have to walk in darkness, because you will have the light that leads to life.”
Jesus said, “You are the light of the world [when you are connected to Him]—like a city on a hilltop that cannot be hidden. No one lights a lamp and then puts it under a basket. Instead, a lamp is placed on a stand, where it gives light to everyone in the house. In the same way, let your good deeds shine out for all to see, so that everyone will praise your heavenly Father."
“Yes, I am the vine; you are the branches. Those who remain in me, and I in them, will produce much fruit. For apart from me you can do nothing."