First post on here! I'll be honest and admit, I'm not modelling Irish railways myself but I do build rather a lot of signals in 7mm scale. I have very happy memories of touring the CIE system back in the 80s and 90s when there were many and wonderful semaphores about. Courtesy of a Tyrconnel Models etch, this is my take on a typical stop signal. It's servo operated and LED lit, using the 5v feed (plus a 330ohm resistor) to the servo to power the led.
Cheers
Jon F.