Halogen lamp - AbsoluteAstronomy.com

A halogen lamp, also known as a tungsten halogen lamp, is an incandescent lamp

Incandescent light bulb

The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...

with a tungsten

Tungsten

Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...

filament contained within an inert gas and a small amount of a halogen

Halogen

The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...

such as iodine

Iodine

Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....

or bromine

Bromine

Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...

. The chemical halogen cycle redeposits evaporated tungsten back on to the filament, extending the life of the bulb. Because of this, a halogen lamp can be operated at a higher temperature than a standard gas-filled lamp of similar power and operating life. This gives it a higher luminous efficacy

Luminous efficacy

Luminous efficacy is a measure of how well a light source produces visible light. It is the ratio of luminous flux to power. Depending on context, the power can be either the radiant flux of the source's output, or it can be the total electric power consumed by the source.Which sense of the term is...

(10–30 lm/W). The lamp gives light of a higher color temperature

Color temperature

Color temperature is a characteristic of visible light that has important applications in lighting, photography, videography, publishing, manufacturing, astrophysics, and other fields. The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of...

. Because of their smaller size, halogen lamps can advantageously be used with optical systems that are more efficient in how they cast emitted light.

History

A carbon filament lamp using chlorine

Chlorine

Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

to prevent darkening of the envelope was patented in 1882, and chlorine-filled "NoVak" lamps were marketed in 1892. The use of iodine was proposed in a 1933 patent, which also described the cyclic redeposition of tungsten back on the filament. In 1959 General Electric patented a practical lamp using iodine.

Halogen cycle

In ordinary incandescent lamps, tungsten evaporates from the filament and deposits on the bulb, darkening it. The halogen takes part in a reversible chemical reaction with the deposited tungsten. Tungsten on the bulb wall is attacked by the halogen and forms a gaseous compound, which breaks down in the heat of the filament, releasing tungsten metal to the filament and the halogen back into the bulb. The halogen is then free to repeat the process. The halogen cycle keeps the bulb clean and the light output remains almost constant throughout life.

At moderate temperatures the halogen reacts with the evaporating tungsten, the halide

Tungsten(V) bromide

Tungsten bromide is the inorganic compound with the formula . The compound consists of bioctahedral structure, with two bridging bromide ligands.-Preparation and structure:...

formed being moved around in the inert gas filling. The overall bulb temperature must be higher than in conventional incandescent lamps. The bulb must be made of fused silica (quartz) or a high melting point glass (such as aluminosilicate glass). Quartz being very strong, the gas pressure can be higher, which reduces the rate of evaporation of the filament, permitting it to run a higher temperature (and so efficacy) for the same average life. The tungsten released in hotter regions does not generally redeposit where it came from, so the hotter parts of the filament eventually thin out and fail. Regeneration of the filament is also possible with fluorine, but its chemical activity is so great that other parts of the lamp are attacked.

In this accelerated video, the tungsten-halogen cycle is demonstrated. A tube allows halogen gas to be withdrawn and re-introduced as desired. When switched on, the filament is operating in a vacuum. After a few seconds the bulb is observed to blacken; this is caused by tungsten atoms that evaporate from the filament and condense on the bulb wall. Once completely blackened, the halogen gas is re-introduced into the bulb. It quickly reacts with the tungsten that has been deposited on the relatively cold bulb wall, and transports it back to the hot filament. The result is that the wall is returned to its original clarity. In this experiment the concentration of halogen gas used is higher than normal so as to achieve the rapid clean-up. In a standard lamp, the speed of the halogen regenerative cycle is much slower, but it operates continuously to prevent the bulb from blackening, and to maintain constant light output.

Quartz iodine lamps using elemental iodine were the first commercial halogen lamps launched by GE in 1959. Quite soon, bromine was found to have advantages, but was not used in elemental form. Certain hydrocarbon bromine compounds gave good results. The first lamps used only tungsten for filament supports, but some designs use molybdenum — an example being the molybdenum shield in the H4 twin filament headlight for the European Asymmetric Passing Beam.

High temperature filaments emit some energy in the UV

Ultraviolet

Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

region. Small amounts of other elements can be mixed into doped quartz (or selective optical coating) to block harmful UV radiation. Hard glass blocks UV and has been used extensively for the bulbs of car headlights. Alternatively, the halogen lamp can be mounted inside an outer bulb, similar to an ordinary incandescent lamp, which also reduces the risks from the high bulb temperature. Undoped quartz halogen lamps are used in some scientific, medical and dental instruments as a UV-B source.

For a fixed power and life, the efficacy

Luminous efficacy

of all incandescent lamps is greatest at a particular design voltage. Halogen lamps made for 12 to 24 volt operation have good light outputs, and the very compact filaments are particularly beneficial for optical control (see picture). The range of MR-16 (50 mm diameter) reflector lamps of 20 W to 50 W were originally conceived for the projection of 8 mm film

8 mm film

8 mm film is a motion picture film format in which the filmstrip is eight millimeters wide. It exists in two main versions: the original standard 8mm film, also known as regular 8 mm or Double 8 mm, and Super 8...

, but are now widely used for display lighting and in the home. More recently, wider beam versions are available designed for direct use on supply voltages of 120 or 230 V.

Effect of voltage on performance

Tungsten halogen lamps behave in a similar manner to other incandescent lamps when run on a different voltage. However the light output is reported as proportional to

, and the efficacy proportional to

. The normal relationship regarding the lifetime is that it is proportional to

. For example, a bulb operated at 5% higher than its design voltage would produce about 15% more light, and the efficacy would be about 6.5% higher, but would be expected to have only half the rated life.

Halogen lamps are manufactured with enough halogen to match the rate of tungsten evaporation at their design voltage. Increasing the applied voltage increases the rate of evaporation, so at some point there may be insufficient halogen and the lamp goes black. Over-voltage operation is not generally recommended. With a reduced voltage the evaporation is lower and there may be too much halogen, which can lead to abnormal failure. At much lower voltages, the bulb temperature may be too low to support the halogen cycle, but by this time the evaporation rate is too low for the bulb to blacken significantly. There are many situations where halogen lamps are dimmed successfully. However, lamp life may not be extended as much as predicted. The life span on dimming depends on lamp construction, the halogen additive used and whether dimming is normally expected for this type.

Spectrum

Like all incandescent light bulb

Incandescent light bulb

s, a halogen lamp produces a continuous spectrum of light, from near ultraviolet to deep into the infrared. Since the lamp filament can operate at a higher temperature than a non-halogen lamp, the spectrum is shifted toward blue, producing light with a higher effective color temperature

Color temperature

Safety

Halogen lamps get hotter than regular incandescent lamps because the heat is concentrated on a smaller envelope surface, and because the surface is closer to the filament. This high temperature is essential to their operation. Because the halogen lamp operates at very high temperatures, it can pose fire

Fire

Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....

and burn

Burn

A burn is an injury to flesh caused by heat, electricity, chemicals, light, radiation, or friction.Burn may also refer to:*Combustion*Burn , type of watercourses so named in Scotland and north-eastern England...

hazards. Some safety codes now require halogen bulbs to be protected by a grid or grille, especially for high power (1–2 kW) bulbs used in theatre

Stage lighting

Modern stage lighting is a flexible tool in the production of theatre, dance, opera and other performance arts. Several different types of stage lighting instruments are used in the pursuit of the various principles or goals of lighting. Stage lighting has grown considerably in recent years...

, or by the glass and metal housing of the fixture to prevent ignition of draperies or flammable objects in contact with the lamp.

To reduce unintentional ultraviolet

Ultraviolet

Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

(UV) exposure, and to contain hot bulb fragments in the event of explosive bulb failure, general-purpose lamps usually have a UV-absorbing glass filter over or around the bulb. Alternatively, lamp bulbs may be doped or coated to filter

Filter (optics)

Optical filters are devices which selectively transmit light of different wavelengths, usually implemented as plane glass or plastic devices in the optical path which are either dyed in the mass or have interference coatings....

out the UV radiation. When this is done correctly, a halogen lamp with UV inhibitors will produce less UV than its standard incandescent counterpart.

Handling precautions

Any surface contamination, notably the oil from human fingertips, can damage the quartz envelope when it is heated. Contaminants will create a hot spot on the bulb surface when the bulb is turned on. This extreme, localized heat causes the quartz to change from its vitreous

Glass

Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

form into a weaker, crystalline form that leaks gas. This weakening may also cause the bulb to rapidly form a bubble, thereby weakening the bulb and leading to its failure or explosion, and creating a safety hazard. Consequently, manufacturers recommend that quartz lamps should be handled without touching the clear quartz, either by using a clean paper towel or carefully holding the porcelain base. If the quartz is contaminated in any way, it must be thoroughly cleaned with alcohol and dried before use.

Applications

Halogen headlamp

Headlamp

A headlamp is a lamp, usually attached to the front of a vehicle such as a car or a motorcycle, with the purpose of illuminating the road ahead during periods of low visibility, such as darkness or precipitation. Headlamp performance has steadily improved throughout the automobile age, spurred by...

s are used in many automobiles. Halogen floodlights

High-intensity discharge lamp

High-intensity discharge lamps are a type of electrical lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. This tube is filled with both gas and metal salts. The gas facilitates the...

for outdoor lighting systems as well as for watercraft

Watercraft

A watercraft is a vessel or craft designed to move across or through water. The name is derived from the term "craft" which was used to describe all types of water going vessels...

are also manufactured for commercial and recreational use. They are now also used in desktop lamps.

Tungsten-halogen lamps are frequently used as a near-infrared light source in Infrared spectroscopy

Infrared spectroscopy

Infrared spectroscopy is the spectroscopy that deals with the infrared region of the electromagnetic spectrum, that is light with a longer wavelength and lower frequency than visible light. It covers a range of techniques, mostly based on absorption spectroscopy. As with all spectroscopic...

.

Halogen lamps were used on the Times Square Ball

Times Square Ball

The Times Square Ball is a time ball dropped each year during the New Year’s Eve celebration in Times Square, Manhattan, New York City. The ball is made by Waterford Crystal and electric lights is raised to the top of a pole on the One Times Square building at 6:00 pm and then lowered to mark the...

from 1999 to 2006. However, from 2007 onwards, the halogen lamps were replaced with LED

Light-emitting diode

A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...

lights. The year numerals that light up when the ball reaches the bottom used halogen lighting for the last time for the 2009 ball drop. It was announced on the Times Square website that the year numerals for the 2010 ball drop would use LED lights.

Automotive

Normally available in 12 V, with many also in 6 V and/or 24 V versions.

Single filament, in 55 W and 100 W versions:
- H1
  H1 bulbs
  The H1 is a halogen lamp designed for use in automotive headlamps and fog and driving lamps. It has also been widely applied in emergency vehicle lights.-Origin:...
  
  axial filament, older style base
- H2 axial filament
- H3 transverse filament, heat-resistant cable for "hot" lead
H4 dual-filament headlamp, 55 W to 100 W low beam, high beam varies from 60 W to 130 W
H5 (similar to H4 but it has larger connector)
H7

Architectural

Linear in various sizes and power
- R7S: linear halogen lamp measuring 118mm or 78mm. Also known as a double ended halogen lamp.

Dichroic and plain reflector spots. Higher efficiency versions using IRC (infrared reflective coating)
Incandescent light bulb
The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...

technology are 40% more efficient than standard low voltage halogen lamps

Home use

Halogen multifaceted reflector bulbs are widely available. The most common format is MR16, which is available in 10–50 W power ratings (150–800 lumens).

With the help of some companies such as Philips

Philips

Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....

and Osram Sylvania

Osram Sylvania

Osram Sylvania Inc. is the North American operation of lighting manufacturer Osram GmbH, which is owned by Siemens AG. It was established in January 1993, with the acquisition of GTE’s Sylvania lighting division by Osram GmbH....

, halogen bulbs have been made for standard household fittings, and can replace low-efficacy incandescent light bulbs that are being phased out.

Dual pole versions are now being used in standalone lamps and household fixtures. These come in various lengths and wattages (50-300w).

Stage lighting

Tungsten halogen lamps are used in the majority of theatrical and studio (film and television) fixtures, including Ellipsoidal Reflector Spotlights and Fresnels

Fresnel lantern

A Fresnel lantern is a common lantern used in theatre, which employs a Fresnel lens to wash light over an area of the stage. The lens produces a wider, soft-edged beam of light, which is commonly used for back light and top light....

. PAR Cans are also predominately tungsten halogen.

Cooking

The GE Advantium

Advantium

Advantium is a line of fast-cooking electric ovens for household use sold by General Electric. They use both halogen lamps and microwave energy, either separately or together....

patented line of speed cooking ovens utilize up to a 1500 W halogen bulb.

Specialized

Projection lamps are used in motion-picture and slide projectors for homes and small office or school use. The compact size of the halogen lamp permits a reasonable size for portable projectors, although heat-absorbing filters must be placed between the lamp and the film to prevent melting. Halogen lamps are sometimes used for inspection lights and microscope stage illuminators. Halogen lamps were used for early flat-screen LCD backlighting, but other types of lamp are now used.

Disposal

Halogen lamps do not contain any mercury. None of the materials making up the lamp would cause it to be classified as hazardous waste.

History

Halogen cycle

Effect of voltage on performance

Spectrum

Safety

Handling precautions

Applications

Automotive

Architectural

Home use

Stage lighting

Cooking

Specialized

Disposal

See also