For once you were darkness, but now you are light in the Lord; walk as children of Light [lead the lives of those native-born to the Light]. Ephesians 5:8 (AMPC)
Believers are children of Light because our Father God is Light. 1 John 1:5.
What does it mean to walk in the light?
Ephesians 5:9 (AMPC) For the fruit (the effect, the product) of the Light or the Spirit [consists] in every form of kindly goodness, uprightness of heart, and trueness of life.
When we are expressing and exhibiting kindness, goodness, uprightness and truth then we are walking in the light.
Pleasing the Lord, doing what’s acceptable to Him is walking in the light. Ephesians 5:10 (AMPC)
The Word of God is Light. Psalms 119:105. Therefore walking according to God’s Word is walking in the light.