A 4" square aperture specification grade modular housing platform that accepts tungsten-halogen, compact fluorescent and ceramic metal halide lamps. Suitable for 2x6 residential framing or shallow plenum commercial installations. The platform is airtight to prevent energy loss, room drafts, dust marks on the ceilings and reduce sound transmission. Insulation must be kept 3" away from top and sides of the housing. A complete fixture requires three components; a P406TAT housing platform, a 4" lamp module and optical element. Modules and elements may be changed after installation from below the ceiling to provide a variety of lamp sources and optical distributions. The P4MRTAT and P4MRTCP housings come with the MA4MR low voltage MR16 directional lamp module factory installed to reduce installation time but retain the flexibility of the modular platforms.