A German friend of mine asked me this question in relation to the analogy of "light through a prism". It is an important point to explain because the Nicene Creed teaches of the eternal generation of the Son of God by using the following language:
We believe in ... in one Lord Jesus Christ, the Son of God, the Only-begotten, Begotten of the Father before all worlds, Light of Light, Very God of Very God, Begotten, not made; of one essence with the Father, by whom all things were made:
Now the Lord Jesus is described as being "Light of Light" and this most probably came from one of the four "God is" attributes given in the New Testament. Do you know what they are?
* God is spirit (John 4:24)
* God is faithful (1 Cor. 1:9)
* God is light (1 John 1:5)
* God is love (1 John 4:8)
How do we understand what "God is love" means? Do we look for human analogies of love in the family to describe this "God-kind-of-love"? No we do not, because it will be imperfect and therefore it will not responsibly handle the truth concerning the eternal and infinite God. Instead, we must turn to holy Scripture. The Scriptures teach us that God's love is known in the sending his Son and in his Son dying on the cross to make propitiation for sin. Concerning this truth we read that:
John 3:16 "“For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life.
1 John 4:9-10 "In this the love of God was made manifest among us, that God sent his only Son into the world, so that we might live through him. 10 In this is love, not that we have loved God but that he loved us and sent his Son to be the propitiation for our sins".
Now concerning light, the same biblical approach needs to be followed because John the apostle states: "God is light, and in him is no darkness at all" 1 John 1:5. The context of this passage is to contrast the being and attributes of God, which is of light without darkness and sin, with that of the lives of some professing Christians. Now natural light of the sun is created by God, in order to provide heat and light for the created order. Romans 1:20 teaches "For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse" ... but this does not mean that anything in Creation can be used to describe God-as-he-is-in-himself and this includes "natural light". God is not created or natural, but God is spirit!
Now let us consider white light refracted through a prism into the three primary colours of red, blue and yellow and ask the question; does this analogy help to describe that the Trinity is made of one God, who is also three distinct persons? The primary colours can be mixed to make a different colour, for example blue+yellow = green, so that actual colour becomes something else. Immediately we have to ask the question, can God the Son become the Father or something else and the answer is no. Therefore, before we go too far with this analogy, immediately we realise that this illustration has already begun to break down.
I imagine that the desire to use "light through a prism", as an analogy, is a genuine attempt to explain that God is one, yet three distinct persons. However, when you choose colour schemes on your Apple or Microsoft Word documents, they usually show them on a two-dimensional circular image, where it is clear to see it is hard to pinpoint where blue begins and red starts, thus blurring the distinctions. God the Father, is not the Son, the Son is not the Father, the Holy Spirit is not the Father: They are together "One God and three distinct persons". In conclusion, we cannot recommend or support the "light through a prism" as an analogy to explain the doctrine of the Trinity. Instead, let us remain within the boundaries of Scripture and the Nicene Creed (381) to aid us. I hope this helps us all, in order to uphold the truth concerning the Persons of the Triune God.