Before radar, the state of the art to detect approaching aircraft was to look and listen.
Handheld or larger tripod mounted binoculars were used to visually locate aircraft.
If at night, a searchlight such as the museums examples, might be used to locate and illuminate aircraft for targeting. High powered lights were also occasionally used to illuminate ground targets and dazzle enemy troops or positions.
Aircraft could in some conditions be heard before they could be seen.
Acoustic locators used various trumpet shaped devices to focus sound to the operator.
The museum's searchlight on the right was is a WWII German Mod 37 Flakscheinwerfer made in Germany in 1943. It is a 990 Million Candlearc light with a 150cm(59') glass parabolic reflector.. The 200 amp generator is in the lot behind the museum.
We obtained the set from Finland.
The light on the left is an American made General Electric light.