Short arc lamps are usually used in movie theater projectors, searchlights, specialized medical equipment with fiberoptic light delivery means, some stage spotlights ("followspots"), and some scientific equipment requiring an extremely intense light source. The high cost, short lifetime, limited efficiency, and major safety hazards of short arc lamps make them impractical for general purpose lighting.
The arc is about as intense as a welding arc or a carbon arc. One should not look directly at the arc. If your eyes are already adapted to bright light, you may get away with looking at the arc for up to a few seconds with no permanent eye damage - but doing this is NOT a good idea. You won't hurt your eyes looking at the arc through #12 welding glass - but there are other hazards. Filters made for looking directly at the sun will also make the arc safe to look at directly. Most other dark transparent materials will not protect your eyes since they let through enough infrared to risk cooking spots on your retina - an eye damage phenomenon notoriously lacking warning signs.
The arc emits almost every kind of ultraviolet in the book, including large amounts of UV-A, UV-B, and some UV-C. Mercury xenon short lamps tend to be optimized for producing intense UVB and UVC. These different ultraviolet bands are bad for different parts of your eyes. Number 12 welding glass and sun-viewing filters will protect your eyes. However, the UVC, UVB, and the shortest UVA wavelengths can sunburn your skin. Serious sunburn and increased risk of skin cancer may result from significant exposure to this radiation. UVC and UVB are blocked by ordinary glass and tanning range UVA is mostly blocked by ordinary glass, but for other reasons below it is HIGHLY RECOMMENDED to only operate short arc lamps in fixtures designed and made for them by qualified personnel - typically engineers and technicians who work for the fixture manufacturers.
The shortest ultraviolet wavelengths emitted by short arc lamps can generate ozone. Operate the lamps in an adequately ventillated area. If you can smell the ozone, it can noticeably irritate your lungs within hours.
Short arc lamps operate at red-hot temperatures of up to 900, sometimes even 1050 degrees C (approx. 1650-1900 degrees F) and contain very high pressure usually in excess of 10 atmospheres and often near or over 20 atmospheres, and in a few cases 50-plus atmospheres. They can explode. Rarely, but who knows how rarely, they explode when nothing can be detected as wrong. If operated in any way other than as specified or past their intended life expectancy, the risk of explosion increases. Explosions can be dangerous since they can result in red-hot (or hotter) pieces of glasslike quartz being shot out in all directions, possibly with considerable force. These lamps should only be operated in fixtures made for these lamps and designed to contain a lamp explosion. Some of these lamps contain mercury, so you might not want one to explode in your home even if there was no risk of fire or red-hot glass shrapnel.
Some short arc lamps require forced air cooling. Some larger ones require water cooling. This is another reason to operate them only in fixtures designed for the particular lamp being operated.
Many short arc lamps have pressure well above atmospheric pressure even when they are cold. You don't want to drop one and have it break.
Many short arc lamps have recommended protection shields shipped with them in case they break during shipping or handling. These shields have increased importance for handling used lamps, which can be weakened by effects of aging. A used short arc xenon lamp is shown to explode from even gentle handling in this YouTube video.
The pressure in the bulb, even at room temperature, caused fragments of the bulb to cause skin injuries. Severe eye injury could have occurred. Some short arc xenon lamps come with recommendation to use full body protection while handling.
Short arc lamps have quartz bulbs operated under stress at high temperature. The usual halogen lamp rules for bulb cleanliness apply. Carbon deposits can absorb light and make hot spots. Traces of any sort of ash, salts, metal oxides, or alkalis can leach into hot quartz and cause strains which can weaken the quartz. You should not touch the bulb. If you touch the bulb, you can clean it with alcohol so that no skin oil traces are left on the bulb. It may also be a good idea to rinse the bulb with distilled water.
Do not operate a short arc lamp that has been scratched or chipped.
Short arc lamps should be operated only at the wattage they were designed for
and with the type of current they were designed for. Overpowering them is
obviously bad. Underpowering an arc lamp can also be bad, since a
slightly-too-cool electrode does not emit electrons easily, and the voltage drop
in the cathode region of the arc increases and causes positive ions to hit the
cathode harder, which "sputters" off cathode material. This will discolor the
bulb and may cause the bulb to overheat or have an abnormal temperature gradient
somewhere and could make the bulb explode. Discolored bulbs as well as
abused electrodes can really overheat if operated at full power.
Some short arc lamps are designed for AC, and typically have two identical main
electrodes. Most are designed for DC and DC lamps usually have two visibly
dissimilar main electrodes. Operating an AC lamp on DC will overheat and/or
excessively age at least one electrode. Operating a DC lamp on AC will overheat
and/or excessively age at least one electrode, as will operating a DC lamp
with reversed polarity. Some DC lamps require well-filtered DC for full life
expectancy and for proper function of aging electrodes. Aging electrodes
have limits in the peak rate at which they can emit electrons without
overheating or sputtering, and peak current has to be minimized. Excessive
peak current may accelerate aging of electrodes that are in good shape.
Short arc lamps may have to be operated in a specific position so that convection currents - internal and external - don't cause vulnerable parts of the lamp to overheat. This is another reason to use them only as directed in proper fixtures designed specifically for the lamp being used. Folllow all directions that come with the lamp and all directions that come with the fixture.
With all this trouble and the high cost and short life expectancy of short arc lamps, it is no wonder why they are only used where there is no substitute for a small, very intense arc. Short arc lamps are not good toys for casual experimenters.
Posted in sci.optics and sci.electronics.misc by John Byrne
Please be VERY careful with any high pressure Xenon lamps, especially the
short-arc type. Even when cold, they still represent a very significant
explosion risk, with cold fill pressures of 10-25 atmospheres. You drop one
of these on the floor......... think of a hand-grenade! (and yes, It has
happened to me!)
All xenon lamps are now shipped in multi-layer protective packaging, with
many warnings about the use of FULL face and body protection BEFORE even
opening the the box!
As to the operation of these lamps, don't try to make your own gear, it's just
too expensive, and the ignition voltages required sometimes exceed 75kV.
UV is a definite problem, and also the explosion risk, so operation of this
lamp will require a protective enclosure.
Mercury vapor short arc lamps contain a low pressure gas fill, typically argon,
plus mercury. These lamps start easily without multi-kilovolt starting pulses
but require a warmup period and have poor color rendering. The spectrum consists
mainly of mercury lines but also has some continuous spectrum. The color rendering
is better than that of a general-purpose unphosphored mercury lamp, but not good
enough for color film projectors since the spectral output is low on red.
At least many mercury short arc lamps are referred to as HBO lamps and/or have
HBO in their part numbers.
A recent variant of mercury vapor short arc lamps is the UHP lamp developed
by Philips. UHP stands for "ultra high pressure". The pressure during
operation is approx. 200 atmospheres. This extreme high pressure combined
with extreme power input per unit volume of the arc results in sufficient
continuous spectrum content in the spectrum to achieve usable red spectral
content in small digital projectors.
Xenon short-arc lamps do not require a warmup period and have excellent color
rendering. The color is an icy pure to very slightly bluish white, with a color
temperature usually in the low 5,000s Kelvin. UPDATE 11/27/2021: I have been
aware of xenon short arc lamps having color temperature in the 4000s K. 5000 to
low 5000s K is about the color of noontime tropical sunlight with clean air.
The visible spectrum is almost entirely continuous spectrum, with faint visible
xenon lines. Near-infrared xenon lines are more significant and detract somewhat
from the efficiency at which visible light can theoretically be produced.
At least many xenon short arc lamps are referred to as XBO lamps and/or have
XBO in their part numbers.
Mercury-xenon short arc lamps are a compromise between mercury and xenon in both
advantages and disadvantages. These lamps contain xenon at a pressure around 1
atmosphere (when cold). When started, there is significant light from the xenon
arc. Warmup may take something like a minute, at which time full light output is
achieved. The spectrum has both significant continuous spectrum from xenon and
moderately strong mercury lines. The color and spectrum are somewhat like that
of a "daylight" fluorescent lamp, except the yellow mercury line is stronger
with the still-high mercury pressure and this makes the short arc lamp not
quite as blue nor have quite as good color rendering as the "daylight"
fluorescent lamp.
In addition, shortwave and mediumwave ultraviolet wavelengths of mercury can
run much stronger than usual fior high pressure mercury vapor lamps. The
high amount of power per milligram of mercury vapor in the arc favors arc
temperature a few hundred degrees K higher than usual for high pressure
mercury vapor lamps and increased UV output. Mercury-xenon short arc lamps
have use in some industrial applications requiring ultraviolet wavelengths at
extreme intensity.
Some short arc lamps have only the two main electrodes. Others have a third
electrode for applying the starting pulse.
In most short arc lamp fixtures, current limiting is achieved with an inductor.
Some newer fixtures have electronic ballasts. Since the voltage across the
arc is typically low compared to the line voltage, an inductor ballast
will allow nearly constant current to flow through the lamp even if the
voltage across the arc changes due to aging or warmup. Some electronic
ballasts provide more nearly constant power, and the lamp does not overheat
as badly if the arc voltage rises due to aging electrodes.
Pseudoseries triggering is easier to accomplish with DC lamps than with AC
lamps. In pseudoseries triggering of a DC lamp, a diode or several diodes
are in series with the lamp. These diodes must withstand the pulse voltage
since they prevent the main part of the ballast from shorting out the
starting pulse. The starting pulse device, typically a low power very high
voltage transformer of one kind or another, is connected directly across the
lamp and has reasonably high impedance so that it is not adversely affected
by the main voltage. The starting device ionizes the lamp, and then the
main current flows through the diode(s) and the lamp.
Once the arc is established and the lamp is warmed up, the voltage across
the arc is quite low - often around 30 volts. Very high pressures are
required just to get the voltage drop of a short arc that high.
Short arc lamps have limited lifetime, typically a few hundred to a thousand or
two hours. Any evaporated electrode material will darken much to all of the
inner surface of the bulb. This is unlike conventional discharge lamps which
have the electrodes in the ends of a longer arc tube so that only the ends and
not most of the arc tube are discolored. Metal halide lamps may also have some
sort of a halogen cycle that keeps the inner surface of the arc tube clean, but
most short arc lamps do not have halogens since halogen vapors cause starting
to be even more difficult than it already is. In addition, halogens have some
effect on the hot quartz which is already stressed enough as it is. This can
result in silicon deposits on the electrodes and silicon can be vaporized from
the electrodes onto the inner surface of the bulb, adding discoloration.
HMI lamps are special high intensity metal halide lamps used in some
followspots and are sometimes used for shooting movies. Larger multikilowatt
HMI lamps used in moviemaking have a spectrum with a very large number of
lines, and the visible spectral content is close to that of noontime sunlight.
HTI lamps are a particular variation of HMI lamps. Although the arc in
an HMI lamp is intense, it is not as small and concentrated as the arc in
mercury and xenon short arc lamps. In fact, "HMI" literally means
"hydrargyrum (mercury) medium-arc-length iodide". When maximum light
concentration is required, "true" short arc lamps based on mercury and/or
xenon are used.
You will see hundreds of records, each for various lamps, mostly
HMI, HTI, other specialty metal halide, and ones for HBO (mercury short
arc) and XBO (xenon short arc). Click on the first item in the line (the
Sylvania catalog number) and you can get a brief spec sheet with info
such as wattage, life expectancy, lumen light output and sometimes even
arc voltage and arc current!
If their site changes enough to make the above link fail, hit the one
below after seeing here what to do:
1. Hit their link to the General Lighting Product Catalog (including
photo-optic).
Now that you know what to do there, Go
For It!
Philips, who also makes
short arc lamps.
Advanced Radiation Corporation, a
manufacturer of short arc lamps.
Advanced Strobe, formerly ORC,
makes short arc lamps.
Note that I discourage casual experimentation with short arc lamps because
of their high cost, numerous hazards and generally short life expectancy.
Please read my Copyright and authorship info.
Short arc lamp types
Short arc lamps can be mercury vapor, xenon, or mercury-xenon.
Xenon short arc lamps have the drawback of requiring very high voltage
starting pulses around 30,000 volts. The actual voltage requirement varies
with what model lamp is used.Short arc lamp operation
A ballast is required to limit the current flowing through the lamp and also
to provide any necessary high voltage starting pulses.
If the lamp has a starting electrode, the high voltage pulse may be obtained
from simple, inexpensive circuitry. If a lamp with only two electrodes
requires a high voltage pulse, then series triggering or pseusoseries
triggering is required.
In series triggering, the secondary of a transformer that generates the
high voltage pulse is in series with the lamp. This transformer may be the
current limiting choke, with the secondary being the main winding and the
primary being an auxiliary winding used only for high voltage pulse generation.
With xenon lamps, the necessity of making a ballast main winding withstand
30,000 volt pulses can increase the cost of producing such ballasts.
Pseudoseries triggering has its own drawback with pure xenon lamps. A
diode stack that withstands 30,000 volts can drop 20 to 30 volts when the
main lamp current is flowing, which is almost as much voltage as the arc
normally has across it. The diode stack would consume almost as much power
and make almost as much heat as the lamp does.Limited efficiency and lifetime of short arc lamps
Short arc lamps are not as efficient as general purpose high intensity
discharge lamps. Since the voltage across the very short arc is low, a
high percentage of this voltage is electrode losses. The voltage across
the arc may only be around 30 volts. The electrode losses are typically a
10 to 15 volt drop, so nearly half the power delivered to the lamp is wasted
heating up the electrodes.
Even after allowing for electrode losses, a xenon short arc lamp is less
efficient than theoretically expected for a 5000 to 5500 Kelvin blackbody
radiator, since the xenon arc has strong near-infrared lines. Secondarily,
some of the power delivered to the main body of the arc is conducted and
convected from it as heat instead of being radiated.
Thermal conduction losses can be significant for lower wattage short arc
lamps. This loss is not as bad as it is in general purpose high intensity
discharge lamps since the arc is shorter, but is still in addition to the
horrendous electrode loss that short arc lamps have.
Expect short arc lamps to have unimpressive luminous efficacies. Xenon ones get
a mere 13 lumens/watt for the 75 watt size, 13-20 lumens/watt for 150 watt
sizes, 35-40 lumens per watt in 1-1.6 kilowat sizes, and around 45-51
lumens/watt in 10-20 kilowatt sizes. Mercury and mercury-xenon short arc lamps
are more efficient than xenon ones but less efficient than ordinary general
purpose mercury lamps. Since the arc voltage is low and current is high,
ballast losses may also be quite significant.
Halogen problems have been overcome to an extent that permits the manufacture
of "short arc" metal halide lamps, discussed in a separate section below.
However, the arcs in these lamps are not as small nor as intense as in short
arc mercury, xenon, and mercury-xenon lamps of similar wattage so these
lamps are mostly considered "medium arc length" and not true short arc lamps.Short arc metal halide lamps (HTI/HMI lamps)
Some metal halide lamps have short arc construction. These include most metal
halide lamps under 100 watts, as well as the HTI and HMI lamps. However, the arc is
larger in a metal halide lamp since the metal vapors in the arc easily glow at
lower temperatures than mercury vapor and xenon do. For this reason, the
arc is less intense than the short mercury and xenon arcs.
Conventional metal halide lamps of lower wattages have been widely
available only since around 1990. The arc tube construction often resembles
that of a short arc lamp. In the Philips 70 watt metal halide lamp, the
arc tube is a small sphere.
The HID lamps used in some auto headlights are metal halide lamps, with
some xenon to give usable light output before they have warmed up. For
more info, look in my Automotive HID Lamp File.Links to short arc lamp manufacturers /
suppliers/etc.
Sylvania
"Photo-Optic" Lamps, with many of these being short arc lamps.
2. Hit "Product Class Search".
3. Make the Product Class "Photo Optic", and the Primary category and
Secondary Category both "All Records".
Please send me any corrections and
suggestions.
Written by Don Klipstein.
Please read my Disclaimer.