“Spotlight to Searchlight,” you say.  “Isn’t a spotlight the same as a searchlight?”  Yes, and No!  A spotlight is usually thought of as a small device that sends out an intense beam into a concentrated spot of light like a flashlight produces.

A searchlight is usually viewed as a much larger apparatus that sends out a more intense shaft of light in the same manner, but its beam of light is much larger and usually travels a much greater distance—like the anti-aircraft searchlights of World War II.  Searchlights of 1,500 million-candlepower, with their light visible for 150 mi (241 km), were not uncommon.

In fact, in the 1920’s the London Electric Co. of Croyton, England manufactured a monster searchlight with a light intensity that that tripled the light output of their blazing beams .  According to the Encyclopedia of Mechanical Knowledge: This searchlight was over 7 ft. in diameter and shot out a brilliant white beam worth over 3,500 million candle power.  Every one of its movements was controlled from a portable controller. The top of the carbon arc searchlight stood about 14 feet above the narrow gauge railway track it is pictured sitting upon below.

This dazzling beacon, as bright as the Sun at the center of its light, was fitted with a parabolic silver-on-glass mirror and high intensity arc, which could be cut off instantly without extinguishing its flame. This made it ideal for signaling purposes.  Its arc burned for about two hours without trimming, and a special arrangement of fan-cooling drew off the hot air and gases resulting from the enormous heat it generated.  Its beam could be elevated 90 degrees, moved quickly when ranging, and slowly when the object was sighted.  These features made this "outsize in searchlights" an excellent tool for anti-aircraft work.

Although a spotlight (also called a spot light) may be used for the same purpose as a searchlight (also called a search light), namely to spot or search out something in darkness, transforming one into the other is usually no easy task because of the expectation that a searchlight should emit an extremely brilliant light.

However, Larry Brian Radka, in his DIY (Do-it-yourself) project, managed to do so when he created a brilliant little carbon arc searchlight—affectionately named “Little Blue”—out of an old spotlight that hardly produced much light at all,

as the photographs above aptly demonstrates.

I purchased this working antique recently on Ebay for $150.00, which sounds like a lot, but old spotlights often bring a much heftier price.  I measured the temperature of the spotlight inside with its front window closed, and it measured 200 degrees Fahrenheit and stabilized after operating for a few minutes.

That's when I realized I would have to install a powerful fan and vent to allow it to use a second sun which could generate temperatures up to thousands of degrees inside the spotlight case.

Note the homemade adjustments I installed in it for its now high intensity carbons—to keep the Direct Current arc centered on the focal point of its 12-inch metal parabolic mirror that replaced its old concave aluminum reflector.  A silver-backed glass mirror seems to have a higher reflective power, but can easily break from the intense heat generated by the arc.  I proved this on my 8-inch parabolic mirror during my self-taught course in the “School of Hard Knocks.”  Another reason for using a metal mirror is to prevent breakage from an abrupt shock.  This is why the military has preferred metal metals.  Note the small round arc light window in the center of the mirror behind the carbons.

I installed this to protect my eyes from its harmful ultraviolet rays while adjusting its blazing carbons.

The peephole glass, viewed through the rear to get a good view for adjusting the tilted positive carbon for more exposure to the focal point of the mirror, was taken from one of my automatic carbon arc microscope-projector lamp houses.  Little Blue's separate manual adjustments for positive and negative carbons protrude below.

They may be ganged, and with the proper sizing (the positive burns up faster) I may decide to using a timing belt to drive them with one of my very slow General Electric 12 VDC searchlight motors, purchased on Ebay for a mere $5 a piece.

Note the 24-volt DC squirrel cage fan that I installed in the back of this searchlight.  Its high-volume air flows around the back of the mirror throughout the case and up through the homemade chimney at the top. This keeps the mirror cool and quite free from the burnt white carbon that likes to latch onto its face.   Nevertheless, the fan's air flow does not prevent the transparent glass cover to get very hot, from its resistance to the intense beam of light blazing through the front of the searchlight.

The DC arc in this little searchlight creates an asymmetric operation and different individual carbon conditions.

A crater usually forms in the tip of the positive electrode, as is illustrated above, and it burns up more rapidly than the negative carbon which is often rounded out into a ball-like shape at the end.

The two often leave a remarkable display similar to the shapes in ancient illustration above, found in the 2000-year-old Temple of Hathor at Denderah, Egypt.  Note the flames rising from the positive crater and direction of the current flow in the arc running from positive to negative.

Apparently the ancient Egyptian priests, like modern electrical engineers,

also believed electric current flowed from positive to negative poles.  In 1904, J. A. Fleming discovered the opposite was true.  See The Electric Mirror on the Pharos Lighthouse and Other Ancient Lighting for many more illustrations and details.

I should also point out here also that the positive electrode nearly always emits more light than the negative–just like the flames in Denderah display above indicates.  In carbon arc searchlights and projection systems, a DC arc is usually used so that most of the light is emitted from only one spot, the crater in the tip of the positive electrode.

The tip of the positive carbon is then precisely adjusted to blaze away in the focal point of a searchlight's parabolic mirror so most of its light is reflected in parallel int0 a sharply focused beam that may reach out several miles, like those monster 60-inch searchlights, used by Allied and Axis powers alike during World War II.  Those brilliant "second suns" or "electric mirrors" allowed flak crews to see bombers high in the sky, miles away.

Nevertheless, above we see my largest homemade power supply—using the case of an old General Radio signal generator case, purchased on Ebay recently for $20.00.  The main features inside are a transformer to reduce the 240-volt AC from my clothes-dryer jack to 120 volts, a high power heat-sunk bridge rectifier, appropriate meters and adjustments to monitor and control conditions, and 50 and 80 amp inductors (purchased also on Ebay) to shift the voltage out of phase with the current.  The result is (unlike many cheap arc welders having a fan but still a short duty cycle) a blazing arc allowing my power supply (with no fan) to run cool as a cucumber, even with a long, continuous 38 amps supplied to the arc.  Ohm's power law applies to pure DC (this DC is unfiltered) and in-phase AC voltage and current.  This issue involves the difference between real and apparent power, a technical subject that I won't get into here.

However, for those of you who have electrified minds, I will include here a handy picture above and a simple schematic below of a much smaller DC and AC carbon arc power supply that I built on similar principals a few months ago for my carbon arc magic lanterns.

This smaller 120 VAC input unit also runs cool as a cucumber but supplies less current.

I can adjust the input voltage (and especially current) to the power supply with the variable transformer pictured above.  I purchased it on Ebay for $17.00 recently, but it cost about $45.00 in shipping.  These old variable transformers normally sell for upwards of $1000.00 now, so I consider this a great deal.

This label, if you can read it, gives you a general idea of its technical specifications.  I originally did not use this external variable transformer (with my attached meters pictured below) but a 230 VAC alternistor (an improved triac) with fuses and variable potentiometer from a piece of factory machinery (purchased also on Ebay) in my big power supply instead.

However, when I installed the unit inside the primary winding of the 5 Kilowatt 250 VAC to 125 Vac step-down transformer inside the original homemade power supply pictured above, I didn't want to be bothered with replacing any of the fuses originally installed in factory arrangement, so I replaced them with 20 amp circuit breakers instead.

That was a big mistake indeed, especially since I only had one and also had failed to properly ground the secondary of its transformer to the case and arc light.  Then the negative carbon fell out of its holder while blazing away and the metal fan enclosure mounted on the back of the searchlight cowl arced over to the power supply case and shorted out the alternistor.  Needless to say, the bright flash almost scared the you-know-what out of me.  After I regained my composure, a little research reminded me that fast blow fuses burn up much faster than circuit breakers kick.  Had I left the original fuses in the factory arrangement with the sensitive alternistor instead of replacing them with circuit breakers, I probably would not have to have bothered with bringing out the big gun above.

Nevertheless, the brute electrical force of this transformer guarantees me that I will feel safer at night—as I scan the neighborhood with an old spotlight that grew into a searchlight.