From ABTT Archaeology Committee notes:
1000W (P40, A1/11) Front of House (Profile) spot, 19 degree max.
P40 lampholder pretilted 7½°, 8-in. diameter ellipsoidal reflector, 6 x 8-in. plano convex lens, beam shaping shutters. Skeleton construction for circle front housing.
Introduced c.1948, replaced 1951 by Patt. 53.

See also Patt.83C/CU: As Patt. 83 but with solenoid selected motor driven colour change.

Nicknamed the "coffin spot" due to it's shape.