Afternoon Robert,
After the inquiry into the Cherryville Jctn accident, which recommended the introduction of a high intensity tail lamp to be on the rear of all trains,
Irish rail decided to introduce two tail lamps for all trains during 1990-1991,
The first type were of a French design and were yellow in colour,they were activated by being placed on the lamp iron-but could be switched off with a carriage key where necessary,
The second type were white in colour and were identical to some BR ones that were being used at that time in the UK-(some of the irish ones even having the BR double arrow on them)
They could be switched on or off with a black switch to the right hand side of the red light,
When the battery ran out a little red indicator went out and the lamp had to be sent back to Inchicore for replacement,
These lamps lasted most of the late 1990s until about 2002 when a new lightweight type of lamp was introduced which had LEDs as the red light and are very effective-they are switched on/off by turning a switch at the back of the lamp-and an LED indicator light is located in the side and when this goes out the batteries can be replaced,
Both white types of lamps can still be seen nowadays on liner/Perway trains-but it's the LED type lamp that is the preferred type.
As regards the rule on the use of the lamps,if one or both failed en route then the train could continue to the next station where there was a stock of spare lamps available.