Searchlight

A searchlight is an apparatus with reflectors for projecting a powerful beam of light of approximately parallel rays in a particular direction, usually devised so that it can be swiveled about.

Searchlights were used extensively for defence against nighttime aerial bomber raids around the time of World War II. As radar was a brand-new technology used only by the British for early warning purposes, anti-aircraft flak cannons required visual targetting; searchlights were used to illuminate aircraft in the sky so that the gunners could see them.