The coronas of these mechanical signal are small and weak. In Trainz, coronas are often high intensity, and not realistic. Remember that the signal lights were originally oil or gas flames, and hardly visible in daylight. This was not important, it is the shape of the semaphore that mattered, and illumination was only intended for the night. In the early days the lamps were not even lit during daytime. With electric lights, the situation improved. During the night, a properly focused lamp only needs a power of a few Watt to be visible over a large distance. The enemy of all this was fog, of course...