This type of lamp is also known as an 'MH' lamp. It is an HID lamp (High
Intensity Discharge), which means it provides most of its light from
the electric arc within a small discharge tube. It
is becoming increasingly popular due to its good quality white light
and good efficiency. The most prominent use of the MH lamp is in stadiums
and sports fields. It is also used widely for parking lots and street
lighting in urban areas. Its competitors include the HPS
lamp, mercury vapor lamp, LPS
lamp, halogen lamps, and LEDs.
MH lamps have advantages over the rest which make it more useful for
certain applications. All
credits and sources are located at the bottom of each lighting page
*More pure white light than the popular HPS lamps,
close to daylight frequencies, which allows it to be used for
*More energy efficient than mercury vapor and halogen lamps,
great lumen output
*Good for indoor (high ceiling areas - "high bay"
applications) and outdoor use due to good light quality
*Expensive per-bulb cost: expensive to manufacture
- many parts to assemble and materials are not cheap
*Light pollution: the light is so bright that it produces much
more light pollution than HPS or LPS street lamps, the whites
from an MH lamp are closer to daylight in frequency.
on MH lamps. 8 minutes. YouTube must not be blocked on your server
and flash plug-ins required.
per watt: 65 (large bulbs) up to 115
(small HP MH bulbs) (25%
of energy makes light, 75% heat)
*Lamp life: 20,000 hrs (when mounted base
10,000 hrs (horizontal mounted)
60 - 90 (depends on brand and chemical compositions)
*Color Temperature: 3000 (warm white)
- 20,000K (blue)
Warm up time: 1 - 15 minutes
uses: outdoor lighting where good color rendering is needed,
television/film lighting, sports fields, car headlights, flood
lights, heavy flashlights, green house applications
1.) How it Works:
The lamp uses mercury vapor to
create the powerful light (like the high pressure mercury vapor) but
includes other metals (halide salts) to improve the color.
Halide is a chemical compound of
a halogen combined with an electropositive element, or in the case of
lamps: a metal. A halogen is a monovalent element which readily
forms negative ions. There are 5 halogens: fluorine, chlorine, bromine,
iodine, and astatine.
'salts' used in the MH lamp include:
(Mercury) - bluish
AgCl - white
AgF - no color
AgBr - pale yellow
Agl - green yellow
MH Lamp Operation (not pulse start)
When the lamp is cold the halides and mercury are condensed on the fuzed
quartz tube. When the lamp is turned on current passed through the starting
electrode and jumps the short distance to the main electrode (see the
diagram below), this is aided by argon gas. The argon gas strikes an
arc at low temperatures. (You can also see the 8 minute video
on this page which includes animated graphics how it works)
2.)After the initial small arc the tube heats up and the mercury is
vaporized. Electric arcs fight to work through the resistance of
a gas, but over time more molecules of the gas become ionized. This
makes it even easier for more electric current to pass through, so the
arc gets wider and hotter. In the lamp as the first arc heats up, it
begins to turn the solid mercury into a vapor, soon the arc is able
to travel through the mercury vapor to reach the othermain
electrode on the opposite side of the discharge tube. There is less
resistance on this path now and current stops flowing through the starting
electrode, just as a river changes course to a path of least resistance,
drying out the previous channel.
After a mercury vapor arc strikes and heats, the halides vaporize and
the halides dissociate. The metal atoms diffuse away from the arc to
cooler areas and recombine with the halogen before they damage any part
of the silica or electrodes. The lamp is now fully warmed up and produces
its white light.
halide work lamps are clearly visible in construction on the world trade
center tower (there are no walls to block work lights yet in this photo)
high pressure and temperature of this light would normally react and
destroy the silica in normal glass. Fused quartz is used due
to a high melting temperature, and by using halogens the destructive
process is stopped.
has the highest melting point of any metal and therefore it makes
the best electrode material. The tungsten is treated with radioactive
thorium (Thl4)(ThO2). This helps increase the life of the tungsten and
halide is a favorite for sports field lighting
glass is used in the outer envelope (bulb) due to its ability
to insulate as well as block UV-B radiation coming from the
arc. The bulb also prevents users from touching and fouling
the fused quartz discharge tube with oil from the skin. The
mercury vapor arc in the metal halide lamp produces UV light.
Borosilicate glass, also known as Pyrex insulates the lamp,
insulating the lamp is extremely important to keep the color
constant. Some halides have a lower vaporization point and will
begin to drop out of the discharge if the lamp gets colder.
The halides are designed in a balance to create the desired
white light, loss of the the Agl halide for example will make
the lamp turn more blue. Stabilizing the MH lamp arc and color
was the main problem that Steinmetz
wasn't equipped to solve in the first lamps of 1912.
is used in the seal of the discharge tube because it does not expand
or soften easy, even under extremely high temperatures. Expansion of
the electrode coming out of the discharge tube would crack or break
the sealed tube which forms a flat seam on each end. Molybdenum is also
highly resistant to corrosion and is also used in high strength steel,
armor and electrical contacts.
halide work lights on the Hudson River. You can clearly see the power
of HID lamps here. Only spot and search lights are more powerful.
Variations and Uses
The first MH lamps
had a large outer envelope. In the last 20 years engineers have
been able to make a smaller MH lamp at higher pressures. The
higher pressure means a higher efficiency as well. Left: 1 cm diameter MH lamp used in a hand held flashlight.
Smaller sized bulbs with
lower wattages have allowed for wider application of uses. The smaller
bulbs are used in hand held flash lights (they are not very popular
since they require a large battery (1+ kilo), but they do make the most
powerful hand held light available).Smaller MH bulbs have an
extremely high pressure up to 700 PSI (4,826,325 Pascal).
International MH lamp: this is a pulse start model, pulse
start is normally used with HPS lamps. It uses an igniter to
create a high voltage pulse. This model has a shield to diffuse
light and prevent damage to the lamp if the lamp explodes (this
can happen at the end of life).
Use in car headlights:
The MH lamp has been used
in Europe for automobile headlights for some time. It recently has recently
become legal to use as an automotive headlight in the US. These lamps
cast a cooler light with a poorer color rendering index than Halogen.
This light is brighter and has created controversy as it may make the
road more dangerous by blinding other drivers. This head light is sometimes
confused with the Sylvania "Bright Star" which is a Halogen
headlight with a blue filter.
Notice the different color
temperatures below. The moving car on the left has an HID light about
6000K (bluish), the other to the right has normal halogen tungsten lamp,
about 3000K. The street lights are a warmer colored metal halide, about
Another kind of metal halide
lamp is the halogen metal iodide or HMI lamp. It is mainly used for
photography since it makes a 5600 K light (matching natural daylight)
and has a great CRI. The lamp has a optimum combination of metal halides
made of rare earth metals. It has a quartz discharge tube with rod-shaped
electrodes made of tungsten and a power supply of high voltage DC. The
external ballast is rather heavy, about 6+ pounds. The light is best
used as a powerful light source at 8+ ft (2 m) distance from the talent.
This light is expensive and in demand among the film and television
industry professionals. 90 lumens per watt.
Diagram of an HMI lamp. The arc discharge tube is inside the larger
outer evelope. A getter is left inside during manufacture to remove
all the impurities left, this helps make a true vacuum. The vacuum insulates
the arc tube, so that it stays hot and colors don't shift. FYI: Iodide
halogen was the first halogen used in the incandescent halogen
The Short Arc metal halide
lamp is similar to the xenon short-arc
lamp in appearance. It is a glass tube with a bulging center bulb
with two tungsten electrodes. The high pressure bulb is made of clear
quartz and boasts over 100 lumens per watt(due to the higher pressure).
The bulb is touted as the "most powerful discharge lamp in widespread
use". It uses a Dysprosium iodide and mercury filling in the tube.
6000 K / CRI 95
If you know who developed the Short-arc MH
lamp please contact us so that we may honor
him/her in our inventor section below.
- Light Emitting Plasma
The LEP is a high intensity
light which is often put in a parallel with the LED. The LEP is not
the same, it is actually a form of metal halide lamp and induction
lamp. It has a high pressure quartz bulb that contains metal halides
and no electrodes. This bulb is nestled in a unit that creates radio
frequency energy and directs it into the bulb. The halides are vaporized
and light is made, on the back side of the quartz bulb is a highly reflective
powder. This light has a potential for longer life than the standard
metal halide because it has a perfectly sealed bulb with no electrodes
penetrating the envelope.
This lamp can be used for
street lighting, film lighting and other applications which need intense
lighting equivalent to the HPS or MH lamps.
Companies: Luxim, Topang
- Using magnetron: up to 40,000 hrs, normally 20,000 hrs.
- Using solid chips
to make the RF: longer than 20,000 hrs.
The LEP is related
to the HEP lamp listed on our
Induction Lamps page.
3. Inventors and Developments
Charles P. Steinmetz
is the first to use halide salts in a mercury vapor lamp. He
used the halides to correct color and was successful, but he
could not get a consistent arc. The complex phenomena of plasma
physics was still being explored. Steinmetz's arc would dance
around allowing the temperature in the discharge tube to drop,
the lower temperatures would stop the halide salts from burning
and the color and intensity of the lamp would shift.
Edison Tech Center
1962Robert Reiling used recent developments in the
high pressure mercury vapor lamp to create the first reliable
MH lamp. A fused quartz discharge tube with molybdenum and tungsten
sealed electrodes were just developed to deal with the destructive
high temps of high pressure mercury lamps. Reiling built on
the work of Steinmetz to complete the work. The MH lamp became
more popular decades later as the price of the lamp became more
Espiau, Chandrashekhar Joshi & Yian Chang invented
the LEP or lighting emitting plasma lamp. (Luxim Corp.) The
lamp could be considered both a metal halide lamp and electrodeless
induction lamp. The lamp has not reached full market potential
yet since it is so new. Also see HEP
lamps which are related. Sunnyvale, California
first MH lamp, illustrating the arc path. The tube was bowed to
follow the arc path because the arc was highly destructive to
glass. This was a lower pressure lamp than the modern MH lamp.
of the first multi-vapors ever put in production, 400 W. An
early MH lamp by General Electric. It had the starting electrode
on the top of the discharge tube, this is why there are two
wires leading up to the top. This design is no longer used.
are presented in the order of chronological development
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Sources: Smithsonian Institute
Lighting a Revolution: Charles Steinmetz's Metal Halide Patent
provided by: Edison Tech Center. Photographer M. Whelan
Schenectady Museum archives Lamptech.co.uk
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