Adoration of the Shepherds, Gerrit (AKA Gerard) van Honthorst; link is to zoomable version on Google Art Project, downloadable file on Wikimedia Commons.
I love this kind of nativity scene, in which the painter has represented the infant as the source of light. Special effects!
Van Honthorst was noted for his paintings featuring lighting effects (some similar to those of Georges de la Tour). He also painted another version of Adoration of the Shepherds with a similar light effect.
Link: Adoration of the Shepherds, Google Art Project