Rendered for 1 hour in Luxrender, to practice its material and blender export workflow (and to make something cool).
HDR by Nick Scarcella, skull model by Benjamin R. Wilson.
HDR: https://gumroad.com/l/QRERD
Skeleton: http://www.badking.com.au/site/shop/featured-home-products/skeleton-model-setby-benjamin-wilson/