φωστήρ denotes something that gives light—typically the sun, moon, and stars as celestial luminaries. Paul uses it metaphorically in Philippians 2:15, urging believers to 'shine as lights (φωστῆρες) in the world,' standing out in a dark and crooked generation like stars in the night sky. In Revelation 21:11, the word takes on a different sense: the glory of the New Jerusalem is described as 'her radiance (ὁ φωστὴρ αὐτῆς) like a most precious stone, like jasper, clear as crystal'—here φωστήρ refers not to a light source but to the radiant brilliance emanating from the city of God.