Korry annunciators are used in many larger aircraft. Boeing often uses (or: used, e.g. in the Boeing 737 classic series) the Korry 318 annunciator. It consists of two 28V white light bulbs (Type 387 T1 3/4 Midget Flanged). The annunciator can be pressed, activating a switch to test the annunciator’s light bulbs. The light bulbs …