|Halogen light bulb|
|Wednesday, 22 November 2006|
A typical halogen lamp comprises a hermetically sealed light emitting chamber having a tungsten filament mounted internally of the chamber. In general, a halogen incandescent lamp utilizes a coiled-coil filament, which is formed into a shorter length than that of a coiled filament. The chamber is typically formed from a light transmitting material such as glass. The chamber also includes an inert fill gas such as xenon at a pressure of about seven atmospheres at room temperature. Tungsten halogen lamps operate on a tungsten-halogen cycle which is a regenerative, continuous process in which a halogen containing tungsten compound is produced when the halide combines chemically with particles of tungsten evaporating from an incandescent tungsten filament. During the operation of a halogen lamp, an equilibrium is established between the formation and decay of tungsten halides from the tungsten vapor from the filament and the mixture of halogen and inert glass. The decay reaction thereby takes place at higher temperatures than the formation reaction, so that the tungsten is re-deposited on the filament. The halogen bulbs are generally grouped into a low-wattage (1-100 watts) single-ended halogen bulb and a high-wattage (101-500 watts) tubular double-ended halogen bulb. The single-ended halogen bulb is generally fitted into a domelike case similar to the light bulb of a flashlight or car light and is mounted in a ceiling or wall for lighting or auxiliary lighting. A halogen infrared (HIR) lamp uses an infrared (IR) reflective coating on an elliptical surface of a double ended quartz halogen lamp to preferentially reflect IR radiation to a filament. A typical halogen torchiere lamp has an upward-facing lampshade mounted atop a long, upright stem. Most halogen torchiere lamps for home use have a double-ended, horizontally-mounted bulb set within the lampshade. Halogen incandescent lamps are frequently used in combination with reflectors. Such lamps may be coated with an infrared reflecting layer on the lamp bulb to decrease the power rating of the lamp, while still retaining high filament temperature. Some halogen lamps, known to as MR style lamps, are provided with precise mirrored reflectors. These lamps can produce round, narrow beam distribution that can illuminate the entire height of an object. Typical halogen worklights have a lamp housing with an interior bulb chamber that is lined with an internal reflecting surface, in front of which are disposed one or more halogen bulbs. Such worklights are typically operated at the nominal voltage of the electric utility mains at power levels ranging from around 150 Watts at the low end to 600 Watts or greater in a single lamp housing. For automotive headlight reflectors, halogen lamps are usually used that form a closed unit with the reflector envelope preventing moisture or dust from getting in. One end of the reflector envelope is sealed with an optical lens and the other end is sealed with adhesive material placed into the gaps between the electrical lead wires of the lamp and the holes formed in the bottom portion of the reflector envelope.
The tungsten filament is heated by electric current during operation of the lamp. During operation of the halogen lamp, the tungsten filament is heated to incandescence by the passage of electrical current. The lamp's lifetime is based on the integrity of the filament. Once the filament burns out, the lamp no longer operates. While the lamp is operating, heat produced by electric current in the filament induces evaporation of the filament. The tungsten vaporizes from the filament and condense at the cold spot of the lamp which is typically located on the wall of the light emitting chamber. The condensed tungsten causes the chamber wall to progressively blacken during the life of the lamp which undesirably reduces the light output of the lamp during its useful life. The filament is continuously evaporating during operation of the lamp and, when the diameter of the filament reaches the critical point, the lamp burns out. A higher current flow in the filament results in a more rapid evaporation. In order to preserve the lifetime of a lamp having a tungsten filament during operation wherein the lamp may be turned on and off frequently, it is known to use a current limiter such as an NTC (negative temperature coefficient) thermistor to suppress the initial inrush current while providing negligible electrical resistance once the filament has heated to operating temperature. Due to the temperature dependent operating characteristic of the thermistor, the thermistor must be allowed to cool down in order to restore its resistance to the appropriate value for reactivation of the lamp. In order to prevent a fire caused by a foreign object which happens to make contact with the hot halogen bulb, the tubular double-ended halogen bulb must be shielded by a protective case. A regular halogen lamp control circuit assembly is generally comprised of an electronic transformer, and a light intensity regulator. The light intensity regulator comprises a variable resistor, and a TRIAC. When the variable resistor is adjusted, a signal is sent to the electronic transformer to control its output, so that the intensity of light is relatively adjusted.