The 90th Searchlight Regiment, Royal Artillery, was a short-lived air defence unit of the British Army during World War II.

Regimental Headquarters (RHQ) was formed at the HQ of 3rd AA Brigade at Orangefield House, Belfast, Northern Ireland, on 25 March 1941.

This layout was an attempt to improve the chances of picking up enemy bombers and keeping them illuminated for engagement by AA guns or night fighters.

[4][5][6] Later SLC radar became more widely available and towards the end of 1941 the lights in Northern Ireland were redeployed singly to form a 'killer belt' primarily to assist night fighters.

[13] With the lower threat of attack by the weakened Luftwaffe, AA Command was forced to release manpower for the planned invasion of Normandy (Operation Overlord).