Lamp holders are designed to fit specific light bulb sizes and cap types and they will not fit any others, so always check this carefully. Amongst the most widely used bulb types are:
What is a GLS bulb? General Lighting Service bulbs feature the familiar, basic, pear-shaped design that has been in use for more than a century. They may have either bayonet or screw caps.
Compact fluorescent lamp bulbs are the energy-saving successor to traditional bulbs. Instead of a burning filament, they contain mercury vapour which emits ultraviolet light in response to electrical current. This UV light, in turn, triggers a coating of phosphorus within the bulb to glow, emitting light. Typically, CFL bulbs feature various stick and spiral shapes but traditional pear designs are also available.
Light-emitting diode bulbs are the next step beyond CFL lighting. Extremely energy-efficient and with long lifespans, they provide instant-on lighting. They are built around a semiconductor, a device with electrical conductivity halfway between metal and insulation. This emits light in response to electrical current.