MR11 lamps are regularly used in place of standard compact incandescent light bulbs for applications including residential lighting and retail lighting. MR11 lamps were originally designed for use in slide projectors. They are well suited to a variety of applications that require directional lighting of low to medium intensity, such as track lighting, recessed ceiling lights, desk lamps, pendant fixtures, landscape lighting, retail display lighting and bicycle headlights. Low heat and power consumption and non-polarised AC/DC operation over a wide voltage range 10.5 ~ 18 volts as a standard 12 volt version, allows a wide range of usage. Quoted average rated life given by manufacturers is typically 30,000 - 50,000 hours. This amounts on average to 1250 - 2080 days of continuous operation, or roughly three to six years.
Fixtures designed for halogen MR11 lamps that use electronic power supplies may need to be retrofitted with "LED-compatible" power supplies. This is because these electronic power supplies require a minimum power lamp in order to function, and the LED lamps may be below this power. Fixtures that use magnetic transformers can generally be used with LED lamps without modification.
Unlike halogen MR11s, LED lamps do not have the multifaceted reflectors that give MR11s their precise beam control in a variety of beam spreads. The optics of the LED(s) controls the beam.
The quality and color temperature of the white light produced by LED lamps varies. Many tend towards the blue end of the spectrum, being even "cooler" than fluorescent. Because of these variations, some MR11 compatible LED lamps create significantly more natural looking light than others.
The least efficient of these lamps produce about 26 lm/W (lumens per watt), which is similar to the efficiency of halogen MR11s. The most efficient of these lamps available today produce about 70 lm/W, which exceeds the efficiency of compact fluorescent lamps.
In terms of total luminous power, such lamps range from being significantly less powerful than their halogen counterparts, to being comparable to the lower power halogen MR11s. The brightest available halogen MR11s are still significantly brighter than the brightest available LED versions. (Wikipedia).