Searchlight
Searchlights can be used in missions where the rules for night fighting are used (see page 134 of the Warhammer 40,000 rules). They allow one enemy unit spotted by the vehicle to be fired at by any other Imperial Guard units in range that have a line of fire. However, a vehicle that uses a searchlight can be fired at by any enemy units in their next turn; they can see the light shining in the dark.