The MR11 bulb is part of a range of light bulbs known as Multifaceted Reflector typically referred to as MR or GU4. Traditionally these bulbs were designed to be used in 35mm slide projectors where a small bulb and directional lighting is required. Due to these features the MR11 LED bulb has evolved to be ideal for both domestic and commercial lighting. The physical diameter of an MR11 bulb are 1.375 inches or 34.9 mm, however they use the same 2 pin fitting and socket as the more widely used MR16 or GU5.3 bulb. The majority of LED MR11 GU4 bulbs are low voltage operating at 12V and require a transformer of LED driver.