Psalm 119:130 (NKJV)
Some lights have an adjustment on them that allows you to make the light shine brighter, or you can turn the light down to make things dimmer. Usually, people want more light rather than less, especially if they want to have a good view of what they are looking at, or even if they are reading something. If the light is dim, then you need to increase the amount of light that is being generated. By turning the light down, or even turning it off, you would have less light available, and that could be a problem.
In the Bible, light is often associated with understanding, as we see in Psalm 119:130. God's Word gives us light; God's Word gives us understanding. If we looked at this in the opposite way, so to speak, you could say that not having God's Word means you do not have light or understanding. There are many things you can read, hear, or study, but if those things are not based on God's Word, you would actually be reducing the amount of true light and understanding that you have.
Without the light and understanding of God's Word, and continually being in that light, and also increasing the light, we are really in the dark and in danger of our understanding being diminished. There are a lot of things someone could learn about that would bring knowledge, and even some wisdom, but it is God's Word that gives us the light and understanding we need to recognize what is true and false, to live the life God has called us to live, and do the things that God has called us to do.