MR16
A multifaceted reflector (often abbreviated MR) light bulb is a reflector housing format for halogen as well as some LED and fluorescent lamps. MR lamps were originally designed for use in slide projectors, but see use in residential lighting and retail lighting as well. They are suited to applications that require directional lighting such as track lighting, recessed ceiling lights, desk lamps, pendant fixtures, landscape lighting, retail display lighting, and bicycle headlights. MR lamps are designated by symbols such as MR16 where the diameter is represented by numerals indicating units of eighths of an inch. Common sizes for general lighting are MR16 (16⁄8 inches, 51 mm) and MR11 (11⁄8 inches, 35 mm), with MR20 (20⁄8 inches, 64 mm) and MR8 (8⁄8 inch, 25 mm) used in specialty applications. Many run on low voltage rather than mains voltage alternating current so requiring a power supply.
GU10 is a bi-pin connector designation. A common derivative of the MR housing is GU10 (G for glass) which is a lamp cap fitting format created by Havells Sylvania in 1997. GU10 is distinguished from the MR lamps by the U-shaped ceramic base mount with a 10 mm (pin center-to-center distance) 2-pin bayonet mount and operating under mains voltage rather than lower voltage.
The MR16 lamp was first sold in 1965. Emmett H. Wiley of General Electric (USA) was awarded patent #3,314,331 for a miniature reflector lamp in 1967. The innovation was using the lamp rim, rather than the base, as the reference plane for focusing. This allowed more flexible electrical mounting arrangements and more precise focussing. Note that this lamp was not "multifaceted"; faceted reflectors were introduced in 1971.
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