[ECML43]

This applies to all modern trains.
What's the rule with marker lights on trains? Most trains are fitted symetricly (my spelling's not itself today) with a pair of white front marker lights, a pair of red rear marker lights, and in most cases, a pair of bright headlights. During the day when I do all my trainspotting, all trains seem to have both the marker lights on, but only the right hand headlight on. In fact, some earlier inner suburban trains are only fitted with a right hand headlight e.g: classes 313/4/5. but faster and more modern trains have one on either side. which brings me to ask: what are the rules about when to use which headlights?

(i'd prefer to have a brief answer rather than a link to some complicated page on rules)