Most dispatchers will use a 'Halo' lamp during darkness, which can display red or green as well as white. A red lamp isn't mandatory to stop a train however, as the rulebook also allows 'any other light waved violently'. But anyway, yes it is largely to do with a dispatcher or other person on the platform waving at you to stop, although of course that isn't applicable at every station. Where a dispatcher is provided they are also required to watch the train clear the platform. Again, you could argue the toss as to whether it is worthwhile, but clearly those who set the rules consider that it is. People do run alongside moving trains at times, and have in the past been killed after slipping down the gap. Only recently I witnessed an HST come to a grinding halt after some plonker on the platform ignored the dispatchers yelling repeatedly to stand clear of the departing train. It does happen, and the quicker it is dealt with the better for all concerned. I have no problem with spending a few moments standing by my doors!