A lamp bulb consists of a fine coil of tungsten wire, called a filament, enclosed in a clear glass envelope from which all air has been removed. Passing a current through the filament raises its temperature to a white heat and causes it to give off an incandescent light. Removing air from the glass envelope prevents oxidation of the filament when it is in operation, and increases the filament life.
In high wattage bulbs, particles of tungsten can boil off the filament, even though the air is removed, and eventually cause filament failure. To prevent this, the glass envelope is filled with an inert gas - such as argon - which does not react with the tungsten, and this slows the boiling off of the filament.
To further increase filament operating temperature and increase light output, some bulbs have a hard glass or quartz envelope which is filled to a mild pressure with iodine or halogen gas. Any tungsten that is boiled off by the high temperature is kept in suspension by the gas and is deposited back on the filament to extend filament life. Commonly used in headlights, these are referred to as Quartz Halogen, Quartz Iodine or Tungsten Iodine lamps.
The lamp circuit wiring is connected to the bulb by means of spring contact plungers or by blades which touch the bulb contacts, or by electrical terminals held in place by friction. The filament of a single contact bayonet type bulb has each end connected to a stem. One stem is connected to the lead contact at the base and the other is connected to the bayonet cap. When connected to an electrical circuit, current flows through the filament via the lead contact and the cap causing heat and light.
The bayonet pins on the cap are used to lock the bulb in position against the spring loaded terminal in the socket. Some bayonet type bulbs have two separate filaments in the one envelope.
Each filament has a different light output and is operated by separate circuits, usually in a stop-light/tail-light combination. Two lead contacts at the base provide the input connections to each filament and the other ends of the filaments are connected to the cap to allow the circuit through the filament to be completed. The bayonet pins are offset. This ensures that the correct filament is inserted in each circuit.
Instrument bulbs usually press into place and are called wedge or capless bulbs. The stems of the filaments extend out of, and a small distance up, the glass envelope.
In festoon type bulbs the filament is connected to a metal cap at each end of the bulb. Two metal strips hold the bulb in place in the lamp holder and conduct the current through the filament.
Lamps
Commonly referred to as 'light bulbs', lamps are the removable/replaceable portion of a luminaire which convert electrical energy to both visible and non-visible electromagnetic energy.
Incandescent Lamps
The incandescent light bulb was the first type of bulb, and is inefficient at converting electricity to light. About 90% of the energy input is wasted as heat. This excess heat is then dumped into the air which, in warm climates, must then be cooled by ventilation or air conditioning, resulting in more energy wastage. Due to their heat output, incandescent bulbs can cause burns or start fires if used improperly, and tend to have greater glare.
Halogen bulbs
Halogen bulbs are an improved incandescent. Light energy output is about 15% of energy input, instead of 10%, allowing them to produce about 50% more light from the same amount of electrical power. The bulb capsule is under high pressure instead of a vacuum or low-pressure noble gas. As well as being much smaller and having a hotter filament temperature, this causes halogen bulbs to have a very hot surface. This means that glass bulbs can explode if broken, or if operated with residue such as fingerprints on them. The risk of burns or fire is also greater than other bulbs, leading to their prohibition in some places. Halogen capsules can be put inside regular bulbs or dichroic reflectors, either for looks or for safety.
Good halogen bulbs produce a sunshine-like white light, while regular incandescent's produce a light between sunlight and candlelight. People sometimes find them psychologically pleasing over other types of bulbs due to the more natural color, which lights skin tones and other artifacts more accurately.
HID Lamps
High-intensity discharge lighting first came about with the mercury-vapor streetlights, and later the high-pressure sodium ones with their characteristic orange color. Modern ones are metal halide, used in everything from headlights to floodlights, and with a more pleasant color balance. Like fluorescent's, all HID bulbs require a ballast, but they also require a few minutes (or seconds for headlights) to warm up after "igniting". HID bulbs are over 60% and up to 80% efficient.
LED Lamps
LED's are a very recent introduction to the market, and they are still extremely expensive for any decent-sized bulb. They do however last an extremely long time, up to 100,000 hours (compared to around 10,000 for fluorescent and 1,000 for incandescent). These have come about only since the white LED's they use, and in turn the blue LED's which they were based on. It appears that for now these will be most useful and cost-effective in smaller applications, starting with nightlight's. Colored LED's can also be used for accent lighting, even in fake ice cubes for drinks at parties. They are also being increasingly used for Christmas lights, and not just the battery-powered kind. White LED's are about the same efficiency as other fluorescent's, while red ones can be up to 90% efficient.
Source: CDX Global & Wikipedia - en.wikipedia.org
