In vs. 8, Paul says of the Ephesians: "You were once darkness, but now you are light in the Lord." This chapter, taken together with Ephesians 4, is a vivid description of the contrast between the darkness of the lost and the light of Christ.
The fruit of the light is mentioned as goodness, righteousness, and truth (vs. 9). The fruit of darkness? It is fruitless (vs. 11). Christians are called to live in the light.
That is why we live as wise, not as unwise; understanding the Lord's will rather than being foolish; and filled with the Spirit instead of drunk on wine (vs. 15-18).
Paul is very clear that light does not have fellowship with darkness. We cannot have it both ways. "For of this you can be sure: No immoral, impure, or greedy person - such a man is an idolater - has any inheritance in the kingdom of Christ and of God" (vs. 5).