This, with the Collect for Peace, is the other traditional Prayer Book collect for Evening Prayer.  It, too, has origins in Early Church liturgy, variably in Vespers or Compline.  The first American Prayer Book heavily revised the first line of this collect, but it was changed back in 1892.

Lighten our darkness, we beseech you, O Lord;
and by your great mercy defend us from all perils and dangers of this night;
for the love of your only Son, our Savior Jesus Christ. Amen.

This short prayer has stronger impact when paired (as in the classical Prayer Books) with the Collect for Peace.  Our “darkness” and the “perils and dangers of this night” may sound melodramatic to the modern ear, but in the light of spiritual warfare this makes a great deal of sense.  St. Paul wrote, by way of example, “those who get drunk, get drunk at night,” (1 Thess. 5:7) highlighting the analogical connection between nighttime and our sinfulness.  The worshiper is reminded that it is the love of Jesus Christ that is given to us for protection and aid in our most helpless hours.