The surrounding verses use several verbs to describe what the “servants” are doing: “worship” in Revelation 22:3, “see” in Revelation 22:4, and “reign” in Revelation 22:5. In our present world, such activities require light from the sun or a lamp. In the New Jerusalem they will not require these sources because the Lord God himself is their light. So the inhabitants can ceaselessly “worship” and “see” and “reign.”
5 And night will be no more. They will need no light of lamp or sun, for the Lord God will be their light, and they will reign forever and ever.