"Because you cause my lamp to brighten, O LORD my God, my darkness shines." (My translation)
There are a few other references to lamps in the Old Testament, referring to them as guidance (Ps 119:105) or as a metaphor for life (Job 21:17, 2Sam 21:17). There is also a curious case in Ps 131:17 which has strong ties to John 5:35 (John the Baptist as the lamp set up for the Anointed, preparing his path). There are also New Testament references to eyes being the "lamps of the body" (Matt 6:22), but again it ties into the direction metaphor (Your eyes will guide your direction as a lamp). This is supported by Prov 21:4, which states that "haughty eyes and a proud heart" are the lamp of the wicked. One other metaphor connects lamps to searching (Prov 20:27, Lk 15:8). So why this talk about lamps?
It is the LORD who sustains us and guides us. It is he who is the light of the world to bring us out of our darkness and he who can pierce into our darkness to search us. The Light shines in the darkness, but the darkness can not overcome it but instead retreats to secluded places where the light has not yet touched. And so we are to be the salt and light of the earth, to sustain it and to illumine it. Can you feel that light within you? It is God which shines through you if you open your eyes.