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 () and MR11 (), with MR20 () and MR8 () used in specialty applications. Many run on low voltage rather than mains voltage alternating current so require a power supply. History 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. Characteristics Design and construction Most MR lamps consist of a halogen capsule (or, bulb) integrated with a pressed glass reflector with a base conforming to bi-pin GU5.3 standard. The compact size of the MR base allows for much smaller, more discreet fixtures than the incandescent reflector bulbs that pre-dated MRs. The reflector controls the direction and spread of light cast from the lamp. MR lamps are available with different beam angles from narrow spot lights of as small as 7° to wide flood lamps of 60°. Dichroic reflectors Some lamps use an aluminum coating as a reflector. Others use selective dichroic coating that reflects visible light and allows infrared radiation to pass through. This type reduces heating of illuminated objects since less infrared radiation is present in the light beam. However, dichroic lamps must only be used in compatible fixtures that can dissipate the heat. Dichroic lamps must not be fitted to recessed or enclosed luminaires with the IEC 60598 No Cool Beam symbol. Operation The brightness of MR lamps can be adjusted when used with appropriate light fixtures and dimmers. However, the color temperature changes significantly when the lamp is dimmed, shifting dramatically to the warmer end of the