A shell integrator has a hollow transparent body with inner and outer surfaces formed as arrays of lenslets. Each lenslet of the inner surface images a common source region in the middle of the hollow body onto a respective lenslet of the outer surface. Each lenslet of the outer surface forms a virtual image of the respective lenslet of the inner surface at the common source region. One integrator has a light-guide following the surface of the hollow body from an inlet end at a central region of the surface to an outlet end at a rim of the hollow body. The light-guide inlet end is shaped to receive light from the common source region and direct such light along the light-guide. Another integrator is generally elongated, and may be semicylindrical. Any of these integrators may have a stepped surface forming a Fresnel lens.
