The National Electrical Manufacturers Association (NEMA) published NEMA LE 4-2012, "Recessed Luminaires, Ceiling Compatibility." NEMA LE 4-2012 contains definitions, dimensions, and tolerances for recessed luminaires designed to use fluorescent, high-intensity discharge (HID), and incandescent light sources. Drawing that show examples of fluorescent lamps also apply to HID, compact fluorescent, incandescent, and other lamp sources. This standard does not apply to hard metric dimensioned products; soft metric dimensions or direct metric conversions, however; may be applied throughout this standard as one inch equals 25.4 millimeters.

NEMA LE 4-2012 may be purchased in a hard or electronic copy for $69 by visiting NEMA’s website or by contacting IHS by phone at (800) 854-7179 (United States) or
(303) 397-7956 (international), or by visiting global.ihs.com