High & Low Beam headlights ethics or rules?

[Paul of Covington]

   A somewhat related question:

   When riding in the dome in 1963 on the NP, crossing the plains at night, I got the distinct impression that they were running with the headlight off except when approaching crossings.   Was this ever done, or is the low beam so well defined that there was no scatter visible from my vantage point?

[DMUinCT]

BT CPSO 266

DMUinCT:

Any distance involved? Like if there is a long stretch of track and you can see a train ahead of and coming towards you on the opposite track, is there a certain number of feet between the two trains that the lights must be dimmed by?

Also it seems these two statements contradict, unless I misunderstand:

(D) When standing or moving on main track at meeting points.

The headlight must be extinguished when a train has stopped clear of the main track to meet a train. "

That's the General Orders on one of our local railroads, word for word, other roads may be different.    Underway with an instructor hanging over me,  " a northbound is going to come around that curve ahead, be ready to dim as soon as you see his lights,switch lower front corner of the control consel "

[BT CPSO 266]

DMUinCT:

Any distance involved? Like if there is a long stretch of track and you can see a train ahead of and coming towards you on the opposite track, is there a certain number of feet between the two trains that the lights must be dimmed by?

Also it seems these two statements contradict, unless I misunderstand:

(D) When standing or moving on main track at meeting points.

The headlight must be extinguished when a train has stopped clear of the main track to meet a train. "

[DMUinCT]

Metro North (Commuter) Railroad (NY City & CT)  (first thing I was taught)

" Rule 13.  Headlight "

" The headlight must be displayed brightly on the front of every train by day and night.  When an engine is runnning backward at night, a white light must be displayed on the leading end. " 

" The headlight must be dimmed:

(A) While standing or passing through yards where other engines are working.

(B) Apporaching stations where Form M is to be received.

(C) Approaching junctions or terminals.

(D) When standing or moving on main track at meeting points.

(E) When standing or when approaching another train operating in the opposite direction in multiple track territory.

The headlight must be extinguished when a train has stopped clear of the main track to meet a train. "

[BT CPSO 266]

When it comes to the high beams and the low beams on locomotives. Sometimes I see locomotives dim down their lights when they are passing another train. Is this an established rule (like when it comes to cars) or is it just a matter of locomotive ethics? 

If this is a rule, are there specifics?