Few people realize that all 60 inch Carbon Arc
are all 60 years old or older. Ten thousand were made, mostly
up in Europe for WWII. One guess puts the surviving number at about
worldwide. They were built by the General Electric
Sperry Gyroscope for the U.S. Military as Anti-Aircraft
Units. Their original purpose was to aide World War II
anti-aircraft gunnery crews in spotting enemy aircraft during night-time air attacks. These lights
have not been built since 1944. They no longer had a military use after the war having been replaced by the invention of radar.
Photo Courtesy : Jake Brouwer
The largest Carbon
ever built was built was an 80 inch searchlight build in 1903 by
Electric. It was installed on top of the City Hall of University
City near St Louis for the "1904 St. Louis Worlds Fair". This
boasts an output of 1 billion Candle power. It was recently
in 2004 for a Centennial Celebration.
Weighing in at eight tons, the seven-foot tall searchlight rises through the roof of City Hall on an electric elevator. E. G. Lewis, founder of University City and later its first mayor, installed the searchlight at the top of what was then the Women’s Magazine Building. It made its debut on opening night of the World’s Fair, April 30, 1904, from its perch 135 feet above street level. It was said that on a clear night, the 2 billion candlepower searchlight could be seen as far away as Chicago and Kansas City.
Generator Power: 15 KWV nominal - 16.7 KWV max. (15,000~16,700 watts D.C.)
Powered By: In line 6 cyl. "Hercules" Flathead Engine
Generator Engine Fuel: Gasoline (can also be run using Kerosene or Gasohol) 26 gallons
Generator Fuel Consumption: 2.6 Gal per hour
Combined Weight: 6,000 pounds (3 tons, or the weight of 3 Ford Mustangs combined!)
The Beam is made by 2 carbon rods, one positive and one negative, arching within the focal point of a 60 inch
parabolic mirror. The actual light source is only 1 inch in diameter before it is magnified by the mirror.. As the rods "burn" they are automatically fed into the arc. The rods last approximately 2 hours and then are replaced. The flame that is visible during the lights operation, is not actually the source of the light, rather, it is a by-product, produced as a result of the electricity arching between the 2 rods. The flame is the rod slowly burning away as it is fed into the light. The arc draws 150 amps continuously at 78 volts DC, and burns at over 3,000 degrees Fahrenheit. The power is supplied by the D.C. generator which was designed specifically for this purpose.
An Anti-Aircraft Searchlight Battery was used for the detection, location and illumination of enemy aircraft during darkness enabling Gun Batteries to fire at enemy aircraft efficiently. The battery was made up of 2 transport trucks, Searchlight, Control Station, Sound Locator, Power plant, and interconnecting cables.
It took a team of 12 men to operate ONE Searchlight Battery!
The Sound Locator Squad was made up of 5 men
Chief of Section (Sergeant)
Acoustic Correction Operator
The Searchlight Squad was made up of 7 men
Searchlight Commander ( Corporal)
Power Plant Operator /Truck Driver
A Basic (spare man)
The Sound Locator
Note the very large hoses going to the operators heads. The sound was not electrically amplified, but acoustically coupled to the operators ears like the stethoscope a doctor uses to listen to your heart.
Below are early 1927-1935-model sound locators . They had 4 horns. One operator listened to the left and right horn for direction information, and the other operator listened to the top and bottom horns for elevation information. These units were used since the early 20's
Below are Sound Locators used by other Countries
Heat Detecting Locator
This control station was operated by three men. It could manually aim the searchlight by remote control. The control station was placed several hundred feet away the searchlight in order to see illuminated aircraft better. The beam was so bright, if you were right next to the searchlight, you would mostly see illuminated atmosphere in the path of the beam. This distance was also for safety. You do not want to be next to a searchlight pointed into the sky full of enemy aircraft as these lights also make great targets.
Electric Selsyn signals from the Sound, Heat, or Radar
were sent to the Searchlight control station using a selsyn type system
to send signals to the zero locator meters that were on top of the
Two of the operators, looking at zero locator meters, one for direction
and one for elevation, would watch these meters and keep the meters on
a zero reading using hand cranks on the side of the unit. Keeping these
meters set at zero would keep the control station and searchlight
in the same direction and elevation as the locator device tracked enemy
The third man on this station was the observer. With the observers head in a harness, and using binoculars attached to the station, as the station was aimed by the other two men following the zero locator meters, the observer was forced to visually look at the same direction and elevation that the locators were aimed at. Once the observer spotted the enemy aircraft, he would then take full control of the station using the crank controls located in front of him. These controls were directly connected to the same crank controls the two other operators used to aim the station. This would send Selsyn signals to the searchlight so it would track the observers actions. The observer could also throw a switch on the control station so the searchlight could take Selsyn control signal directly from the locator device whether it be a sound, heat, or radar locator.
Finally, the signals from the control station or location
device are sent to the searchlight. Here, the searchlight operator
the light mechanism and generator. This generator powers all the other
equipment as well as the searchlight. The operator assures that
carbons will burn correctly, the beam is focused, and is the one who
the switch to start the arc burning on command given by the control
In the event of a communication failure, he may also control the aim of the light by hand control. This is done by using a long, 10 foot rod with a wheel on the end. With this rod he can walk the searchlight in the direction he wants and turn the wheel to the elevation he wants. The 10 foot distance give him a better view of the object away from the beam path as well as a safer distance from the light in the event of an attack.
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