Photizo (φωτίζω) is the verb 'to give light' — to illuminate, enlighten, or bring something into visibility. From phos (light), it describes the act of illumination whether physical (lighting a lamp) or spiritual (the enlightening of the mind and heart by the Spirit). It is the root of English 'photon,' 'photograph,' and 'phosphor.'
Ephesians 1:18: Paul prays for 'the eyes of your hearts to be enlightened' — spiritual illumination as a prayer request, something only God can give. Hebrews 6:4 uses photisthentas for those who have 'once been enlightened' — suggesting that true spiritual illumination is a genuine work of the Spirit. John 1:9: Christ is 'the true light, which gives light (photizei) to everyone' — a universal illumination through the Logos. In Revelation 21:23-24 and 22:5, God and the Lamb are the eternal light source, so that the New Jerusalem has no need of sun or lamp — the city is photizein by the glory of God and the Lamb. The darkness that once covered the face of the deep (Genesis 1:2) will be permanently displaced.
The entire ministry of the Holy Spirit can be described as photizo — illumination. He takes the things of Christ (John 16:14) and shines light on them in the human heart. Conversion is described as 'called out of darkness into his marvelous light' (1 Peter 2:9). The church's mission is the extension of this illumination: 'Let your light shine before others, so that they may see your good works and give glory to your Father' (Matthew 5:16). Those who have been photizeo-enlightened are themselves to be light-bearers.