Fallen is the sun who gave us light, Our lordly moon is veiled in night. Our beacon fire is dead and cold A hundred waves have o’er it rolled. What could his light and fire avail Against Lord Ráma’s arrowy hail?

In plain words: Vibhishana says their sun and moon, the light of their people, has gone out. All of Ravana's brightness could not stand against Rama's arrows.