Evening gents,
The 1980 Cardiff Division Sectional Appendix refers to them as "fixed beam electric headlights" and the instruction is that all multiple unit trains and locomotives were to be provided with one of these which was to be illuminated when approaching any level crossing between Craven Arms and Pantyffynon, portable "fixed beam headlights" were available at Shrewsbury, Craven Arms, Pantyffynon, Llanelli and Landore for fitting to locos not already equipped.
Interestingly, the next instruction below this refers to Pantyffynon to Abernant and Gwaun Cae Gurwen, where headlights are required on the leading loco during darkness hours, although a Bardic lamp is permitted in case of failure of the fixed beam light.
Phil