Anything that makes things visible, manifest, exposed (see definition for Dark/Shade/Shadow).
Ephesians 5:13 (NKJV) But all things that are exposed are made manifest by the light, for whatever makes manifest is light.
John 3:20-21 (NKJV) For everyone practicing evil hates the light and does not come to the light, lest his deeds should be exposed.  But he who does the truth comes to the light, that his deeds may be clearly seen, that they have been done in God.”
1 Corinthians 4:5 (NKJV) Therefore judge nothing before the time, until the Lord comes, who will both bring to light the hidden things of darkness and reveal the counsels of the hearts. Then each one’s praise will come from God.
1 Corinthians 4:5 (KJV) Therefore judge nothing before the time, until the Lord come, who both will bring to light the hidden things of darkness, and will make manifest the counsels of the hearts: and then shall every man have praise of God.
- Brightness and lamp used for the manifestation of what is inside of God’s people. When this occurs is says that the “Gentiles shall see.” This refers to the fact that unbelievers (natural men) will even be able to see our manifestation. If a natural man can see our righteousness and salvation, that means it’s manifested physically because a natural men (Gentiles) can only see physical things.
Isaiah 62:1-2 (KJV) For Zion’s sake will I not hold my peace, and for Jerusalem’s sake I will not rest, until the righteousness thereof go forth as brightness, and the salvation thereof as a lamp that burneth.  And the Gentiles shall see thy righteousness, and all kings thy glory: and thou shalt be called by a new name, which the mouth of the LORD shall name.
- Brightness used for Jesus being the revealing of who God is.
Hebrews 1:3 (KJV) Who being the brightness of his glory, and the express image of his person…