"Lit is such a Light" is not part of the original Arabic, rather an insertion by the translator. In particular, it is alluding to the previous verse of the Qur'an:
Allah is the Light of the heavens and the earth. The example of His light is like a niche within which is a lamp, the lamp is within glass, the glass as if it were a pearly [white] star lit from [the oil of] a blessed olive tree, neither of the east nor of the west, whose oil would almost glow even if untouched by fire. Light upon light. Allah guides to His light whom He wills. And Allah presents examples for the people, and Allah is Knowing of all things.
Basically, the Light here is a metaphor for Allah Himself, and tying the two verses together as the translator has done implies that Allah's Light is also present in these "houses", here referring to the houses of worship erected in His name (i.e. mosques).