A luminaire has a light source and a shell integrator. The shell integrator has a transparent dome over the light source, with inner and outer surfaces formed as arrays of lenslets. Each lenslet of the inner surface images the light source onto a respective lenslet of the outer surface, and each lenslet of the outer surface images the respective lenslet of the inner surface as a virtual image onto the light source. The dome may be substantially hemispherical. The light source and the integrator may be at an input of a collimator.