WWII German Mod 37 Flakscheinwerfer (Searchlight) and generator
Before radar, the state of the art way to detect aircraft was to listen for approaching aircraft with an acoustic locator. Aircraft could in some cases be heard before they could be seen.
If at night, a searchlight was used to illuminate the planes.
The searchlight is a carbon arc light.
The light was produced by two carbon arc electrodes about 3/4" diameter by 10" long. The electrodes were placed in the steel feed tube in the center of the glass and another tube at the top.
Powered by a 200 amp generator, feeding was automatic as the carbon electrodes were burned.
Note the precision made mirror that is still in pristine condition. These search lights in clear conditions could easily project a light beam 25,000 feet due to the precision workmanship. This example was made in Germany in 1943 and was located in Finland.
990 million candlepower arc light with a 150cm (59") glass parabolic reflector
