This traditional, yet strikingly realistic representation of the visitation of the shepherds puts us in the stable with the shepherds. We can sense the wonder and delight that these astonished rural folk feel in the presence of the newly born, the incarnate Messiah. The incorporation of the baby's shining, bright light speaks to the Johannine theme of Christ as The Light.
Many of Gerard Van Honthorst’s paintings employ the use of artificial and unusual lighting effects, such as the dramatic use of dark and glow in this nativity scene. This emphasis on light stems from Honthorst’s membership in the Utrecht Caravaggisti, the Dutch followers of the Italian painter Caravaggio. But beyond the group nomenclature, Honthorst was given the Italian nickname ‘Gherardo delle Notti’ for his particular use of light and shadow to create moving nocturnal scenes. Honthorst's use of light in the midst of dark night may be better understood when we learn that he had been described by a contemporary as "very reserved and melancholic."  In this Christmas season, may we reflect, perhaps as Honthorst did, upon the great gift of the Christ-child, who brings forth light and hope even in the dark and melancholy corners of our lives.
 http://www.oxfordartonline.com/subscriber/article/grove/art/T0038821Honthorst, Gerrit van in Oxford Art Online