If we exclude the multi-megawatt carbon-arc sky trackers that were made during WWII
What were in detail the most powerful searchlights?
Various websites suggest than common models run at 110 V / 200 A, thus 22 kW. Wikipedia vaguely mentions bigger searchlights with 200 cm diameter, powered by a 120 kW generator, which suggests a power consumption of the arc somewhere between 50 and 100 kW. Such figures have also been mentioned in a book from the fifties for fixtures in large movie studios. Such beasts were necessary for the first colour film stocks with a sensitivity of a mere ISO 16/13°.