In general, LED downlights (hereafter referring to the integrated type) are self-contained lighting systems that are designed for recessed installation through retention systems, such as torsion springs and friction blades, without using additional mechanical structures. These luminaires typically come with a fixture-as-heat-sink design. The aluminum housing works simultaneously as the heat sink and is exposed in the plenum space for maximum convective heat transfer.
In North America however, downlight luminaires are installed in dedicated housings available in either new construction or remodel units which are designed and constructed as per the UL1598 standards. Remodel recessed housings are designed for retrofit applications where back side of ceiling is not accessible. The aluminum housing can be installed through an opening in the ceiling from below and secured in place by torsion springs and pressure clips. New construction housings are supplied with bar hangers that provide stability and support on joints and T-bar grid ceilings. They must be installed prior to the enclosure of the ceiling so as to coordinate the location of recessed downlights with joists, ducts, wiring, or plumbing that may also be located in the ceiling. New construction housings are divided into four categories depending on whether they can be installed in direct contact with insulated ceilings and whether they are airtight:
Non-IC (non-insulation contact) housings are designed as plaster frames or trays. They are installed in ceilings where no insulation is in contact with the downlight and the insulation must be kept a minimum of 3 inches (7.6 cm) from the fixture. These housings are provided with over-temperature protection to reduce the risk of thermal overload.
Non-airtight IC (insulation contact) housings are constructed in a way similar to the non-IC type housings but allow direct contact with ceiling insulation by enclosing luminaires with a metal barrier or enclosure, commonly known as an IC box. The IC box does not impose airflow restrictions.
Reduced airflow IC (insulation contact) housings can be used where insulation is in direct contact with the housing. An IC box that encloses the luminaire has a construction that reduces airflow but is not guaranteed to any particular specifications (e.g. < 2 cfm under pressure of 1.57lbs/ft²).
Ultra-airtight IC (insulation contact) housings are designed to prevent air leakage from heated or air conditioned into the unconditioned areas. The IC boxes of Ultra-airtight IC housings share a similar design and construction with reduced airflow IC boxes. However the ultra-airtight IC box has caulking applied to all interior joints and the underside of the plaster frame may be gasketed so that airflow is restricted to applicable specifications.
