These verses, like so many in this chapter, are difficult to understand. Some treat them almost literally and render verse 6 as, ‘And it shall come to pass on that day, there will not be light.
Don’t be tempted to derive your happiness from the world and its pleasures. Your light is the light that God supplies and that is what you should keep your eyes fixed on. If you see it less clearly, you are in darkness; if you see it more clearly, you are in the light. Never get confused about what is your source of light and of darkness.