"This standards publication contains definitions@ dimensions@ and tolerances for recessed luminaires designed to use fluorescent@ high-intensity discharge@ and incandescent light sources. Drawing examples show fluorescent lamps. However@ these drawings also apply to high intensity discharge@ compact fluorescent@ incandescent@ and other lamp sources. This standard does not apply to ""hard metric dimensioned"" products. However@ ""soft metric dimensions"" or direct metric conversions may be applied throughout this standard as one inch equals 25.4 millimeters."