Recessed 4" square aperture specification grade luminaire utilizing a field replacable LED array conforming to Zhaga standards for interchangability. Lamp modules and optical elements may be changed after installation providing a variety of light sources and optical distributions. Housing is suitable for 2x6 residential framing or shallow plenum commercial installations. The housing is airtight to prevent energy loss, room drafts, dust marks on the ceilings and reduces sound transmission. Insulation must be kept 3" away from top and sides of the housing. A complete luminare consists of a housing platform, lamp module and optical element. Use where high efficiency, excellent light control and low aperture brightness are demanded.