Recessed 4" square aperture specification grade luminaire utilizing a field replacable LED array conforming to Zhaga standards for interchangability. Optical elements may be changed after installation providing a variety of optical distributions. Housing is suitable for commercial installations and is airtight to prevent energy loss, room drafts, dust marks on the ceilings and reduces sound transmission. 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.