“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

The first LED was probably produced in 1907. During this period Cat's Whisker radios were the only ones available as valves were yet to be commercialised. HJ Round at Marconi Labs connected his cat's whisker to a battery and observed the emission of green light. This was not a commercial proposition as a device based on this principle is in continual need of adjustment. The "Light Emitting Diode" as we know it was invented in 1962 by General Electric,  but was commercialised by Hewlett-Packard in 1968. The 1970s saw the use of red, green and yellow LEDs  as electronic indicators. The first HP calculators used a small array of LEDs to indicate the numerals. Previously Nixie tubes and gas plasma displays were used for this purpose.

In 1995, Nichia, a comparatively small company, produced a high brightness blue LED. Previously, a few blue LEDs had been made, but they were very expensive to produce and too dim to be practical as indicator lamps. Further developments followed, with Philips making white light LEDs using a fluorescent material to combine blue light with yellow light from the LED chip to produce a white light. White light LEDs had also been made by combining a red, green and blue die in one envelope, but these were not particularly bright. Nowadays, LEDs seem to operate by using a UV emitting die and fluorescent materials. These were pioneered by Cree in 2003. Cree's latest products are comparable in efficiency with compact fluorescent lamps in terms of lumens per Watt - a measure of luminous efficiency. Torches and handlamps using Cree LEDs are available from Afrishop.

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. An HID torch is shown at right.

HID lamps are a form of gas-discharge lamp, and like fluorescents, require a ballast. In portable applications and where high efficiency is required, an electronic ballast is used to provide the high voltage required.

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

Fluorescent

Fluorescent lamps became available in the mid 1930s. They consist of a glass tube with heating elements at each end, containing an inert gas at low pressure. The inside of the tube is coated with a fluorescent material.

If a voltage is applied to the heaters, they enit free electrons. If a subsequent high voltage is now applied acroos the tube, there will be a flow of current which will increase until the tube overheats and self-destructs. To prevent this, a ballast is used to limit the current. (In DC circuits a resistor could be used - but it would dissipate as much power as the lamp). Normally, a magnetic ballast is used as a current limiter.

The flow of current in the tube excites the atoms in the inert gas to produce ultra-violet rays. These are converted by the fluorescent coating on the inside of the tube to visible light. (The starter in a fluorescent tube momentarily connects the heaters - once current flow is initiated, there is no futher need to power the heaters externally).

Nowadays, the magnetic ballast is being replaced with an electronic ballast, which is much more energy-efficient. The compact fluorescent lamps now replacing incandescent lamps (by law in many countries) are simply fuorescent lamps with an electronic ballast in the base. These bases are also available separately.

Compact fluorescent lamps (CFLS) are available with lectronic ballasts to operate from 230 volts AC, as well as 12 volts DC. The 12 volt CFLs are suitable for camping and recreational purposes. They may also be used for emergency lighting without the need for a separate inverter.

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.

Conclusion

Lamps not covered yet include mercury-vapour and the various types of lamp used for street lighting. If you have any questions regarding lamps and fittings, please contact us for assistance