Circuitron
FL1 Strobe Flasher

O, Orange LED
Walthers Part # 800-1011, p. 773 Walthers 2012 HO Scale Reference
O scale, $16.95, not currently in stock at Walthers, Expected: Unknown

 
Bright flash, small package, battery operation. Long battery life; six months continuous operation from one AA alkaline cell. Will operate off hearing aid or watch cell. 1/2 x 3/4" high. HO: 1.5V; O: 3V, N: 1.5V.
 
Bright flash in a small package. Long battery life operates 6 months continously from two AA Alkaline cells. Will operate off hearing aid or watch cell. 3.0 volts 1/20 x 3/4" high.