The E27 is an LED light bulb that is the standard medium bulb base in the U.K. The E27 designation refers to the diameter of the screw base and is only slightly different than the E26 designation, which is the standard medium sized base used in the United States.
E27 bulbs are available in a variety of watt sizes, which indicates the power usage of each bulb. E27 bulbs are available in energy-efficient and light dimming models. LED bulbs are commonly thought to last longer than incandescent bulbs and are considered cost effective, although the initial price point is generally higher, as of 2015.