Jhn 9:5 As long as I am in the world, I am the light of the world.
When I might exist within the world order, I exist as the guiding light of the world order.
Lots here in this short verse, including some key ideas that explain the previous verse, which we will get to in the end, but let's go through it step by step.
First, notice that Christ doesn't use the pronoun for "I" (ego) here. This is typical of Christ in the synoptic gospels but uncommon in John, especially when Christ is making a statement about his nature.
Next, though it is invisible in the KJV which seems to contain two "I am" statements, this first "I am" is a form of the verb "to be" that is not a simple "I am."
Christ almost always uses the indicative, present, active form of the verb "to be" (Ist person-eimi, 2nd-este, 3rd person-esti). He uses this form almost exclusively to refer to himself as "I am". He uses this verb even in statements that seem to refer to the past or the future, for example, in Jhn 8:58, "Before Abraham was, I am." Many take this as a statement of divinity, but all we can say for certain is that he is saying something about his present presence in all time.
Here, the first "I am" is not this form. It is the first person present but in the subjunctive voice. This indicates only a possibility "When I might possibly". This is interesting because when Christ makes this statement, he clearly is in the world, living a human life.
So what is Christ saying and why?
The key may be in the Greek word translated in the KJV as "the world." Christ uses this term to refer specifically to "the world order" or, as we might express this idea today "society." At this point in time, Christ made it clear that he was NOT part of the world order. He makes this clear in many places, for example, in Jhn 17:14, "They are not of the world as I am not of the world."
So Christ here is referring to the times and places in human history where he is part of the world order saying that he is a guiding light to society. However, he make it clear that this is not all times and places. It is not some period of time that started with his birth and continues until the end of time. It is a condition that starts and stops at different times and in different places. For example, European society was once Christian but it grows less and less so. However, societies such as S. Korea are becoming much more Christian.
this is why it is best to begin this verse with "when" instead of "as long as." Christ isn't just referring to the current time, that time in which he was on earth. The KJV almost always translates the Greek word used here (hotan) as "when" but it does not do so here.
This brings us to the last verse, Jhn 9:4, where Christ refers to getting work done in the day, but the night starting. This cycle of day and night becomes a metaphor for the shift in society to and from Christian ideals. Where and when Christ was teaching during his life, he changed society, bringing the light. However, as his opponents working for his death, the night started.
The reference to "light" refers to the day, but Christ always uses light as a metaphor for "knowledge." Here the knowing or understanding on which a society is built.
The larger context of knowledge here goes back to the first verse of this chapter. Christ says that the man's blindness is not a punishment but a visible sign of God's power. Christ is the light by which that power can be seen and understood. Without his throwing light on the human condition, we might think that this blindness was some sort of divine punishment.
φῶς "The light" is from phos, which means both "light" and is the metaphor for "knowledge."