E27 is one of the most common bulb sizes on the market. This is the diameter of the thread of the light bulb. So a thread of 27 mm is screwed into the lamp socket.

Many smart lightbulbs have an E27 thread and therefore also fit into most lamp sockets in your home. Various versions are available, such as E27 light bulbs cold and warm white light as well as E27 light bulbs with changeable light color .

Fun Fact: The E stands for Thomas Edison, the developer of the thread.