The National Electrical Manufacturers Association (NEMA) has published LE 4-2006, Recessed Luminaires, Ceiling Compatibility, which has been revised to incorporate a new standard ceiling system introduced since the previous publication of the document. The updated standardized dimensions for recessed luminaires will ensure compatibility with conventional generic ceiling suspension systems-meaning that fixtures will be designed to fit into ceiling systems without causing distortion or misalignment, and will be properly supported in accordance with the national electrical code. In addition, luminaires will be placed in support systems in a symmetrical manner without oversized gaps existing between the fixture and the ceiling tiles or suspension members.

The publication contains definitions, dimensions, and tolerances for recessed luminaires designed for fluorescent, HID, and incandescent light sources, and can be purchased for $56 via or through Global Engineering Documents at