“Bulbs” or “Globes” are some of the colloquial names for electric lamps. The incandescent electric lamp was invented by Thomas Alva Edison in 1879 and patented in January 1880. This eventually consisted of an evacuated bulb with a carbonized bamboo filament, capable of lasting 1200 hours. This filament was selected after searching through thousands of different materials.

Nowadays tungsten-based filaments are used, but filament lamps are being phased out of use because they are inefficient compared to modern lamps based on new technologies.

The fitting or “cap” is the part of the bulb that mates with a connector supplying electricity to the lamp. The earliest connector is the “Edison Screw”, still in use today.

Lamps

Incandescent

Incandescent lamps or light bulbs use electricity to pass a current through a filament, raising it to a very high temperature producing light. To prevent oxidation (“burning”) of the filament, it is enclosed in a glass bulb containing an inert gas at very low pressure.

Much of the electric power supplied to the lamp is converted to waste heat, making this the least efficient form of electric lighting.

Halogen

Halogen lamps use a tungsten filament surrounded by an inert gas and a small amount of a halogen, such as iodine or bromine. The tungsten filament operates at a much higher temperature than in a normal filament lamp and sets up a chemical reaction that prevents tungsten vapour depositing a metal film on the inside of the bulb. Instead of tungsten vapour being formed, the halogen reacts with the tungsten vapour to form a halide. This halide dissociates in high temperture regions redepositing tungsten on the filament and freeing up the halogen. The high temperatures and pressures inside the lamp necessitate the use of a quartz envelope. They can provide more light output for a given power input than normal incandescent and are therefore slightly more efficient.

LED

High-Intensity Discharge

A high-intensity discharge (HID) lamp operates by producing an electric arc between tungsten electrodes in housed inside a fused quartz tube. These lamps became popular in motor vehicle headlights. They are also used to illuminate football stadiums, gymnasiums etc, anywhere where high levels of lighting are required. They are also now available in flashlights and for other portable lighting, where their high efficiency helps to extend battery life.

The arc from a HID light produces UV radiation, so that most HID lamps are enclosed in an outer UV-resistant envelope.

Fluorescent

Fittings

Edison Screw

The Edison screw cap was developed by Edison for his new incandescent lamp. It is said that Edison got the idea for this connector from the cap of a hot-water bottle. This comes in many sizes. The most familiar being the Miniature Edison Screw (MES) used in torch lamps and the 27 mm Edison Screw (ES) used in many mains light fittings. In chandeliers and decorative lights the Small Edison Screw is often used. Large mercury-vapour lamps, street lights etc often use the Giant Edison screw (GES). There is also a Lilliput Edison screw, which you will find in the Mini-Maglite and a “Candelabra Edison Screw” - midway in size between the SES and MES. These are very uncommon in South Africa.

The Edison screw designation is given by the letter E followed by the diameter in mm, as in the following table:

There are differences in size between the European sizes above and the American sizes – for example the E39 and E26 sizes for ES and GES respectively. The abbreviation MES is sometimes used for “Medium Edison Screw” in North America.

Bayonet Mount

The “Bayonet Mount” connector is the familiar “twist and click” fitting used in the majority of homes for lighting before the advent of down lighters with their twist-lock fitting. The advantage of the bayonet fitting is its ability to withstand vibration or loosening due to temperature variations. The bayonet fitting is also less likely to jam or seize in the base.

Bayonet mounts may have one, two or more pins, and there are many custom sizes for special purposes. Here is a table of common sizes.

The suffix d means 2 centre contacts, s means a single contact.

Bipin (Bi-Pin)

This fitting is used principally for halogen lamps and the ends of Fluorescent lamps. This base was invented by Reginald Fessenden for the 1893 World's Fair in Chicago. Edison's arch rival Westinghouse was given the contract for this and Edison refused to allow his patented Edison screw bulbs to be used.

The suffix after the G indicates pin centre-to centre spacing, and a U suffix indicates the pins have two diameters to lock the lamp into place.

Compact Fluorescent

Compact fluorescent lamps without electronic ballast use push-fit rectangular or square fittings.