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Today Most Decoder have many Light Effects but some do not.  Even if the decoder does do light effect, the quality of the light effect can vary.  There are also prototype rules for lights such as Rule 17 that are sometime misunderstood.  This section will attempt to help one understand:

1) how to get realistic light effects
2) understand the differences between the what the prototype does and what modelers sometime do.

Topics in this section:



A lot of people generally limit their understanding of Rule 17 to the dimming of the headlights.  That is an incomplete understanding.  Rule 17 simply involves the turning of the headlight ON or OFF when the engine/train is meeting certain specific operating conditions.  What most people are really thinking of is Rule 17A.   

Rule 17A involves the optional dimming of the headlight is the locomotive supports it.  Rule 17A has a lot more specific operating condition rules when compared to rule 17.

When one reads the rules below, one can easily see that Rule 17/Rule 17A headlight control can never be done correctly automatically.   If one is interested in proper headlight control with or without dimming, then the headlights must be controlled manually by the us just like the prototype is done.

Here are the Rules regarding headlight usage from the 1962 "Uniform Code of Operating Rules":
RULE 17: 

a) The headlight must be displayed to the front of every train by day and by night.  
b) If the standing train is meeting another train, the standing train headlight must be extinguished if it is: 
      b1) stopped clear of the main track.
      b2) at the end of two or more main tracks. 
      b3) at junctions with switches properly lined for the approaching train.  
      It should be left extinguished until the rear of expected train has passed.

RULE 17A: On Engines so equipped, the headlight must be dimmed when:

a) standing on yard tracks.
b) standing on the main track at meeting points after the switch has been lined for the siding.
c) approaching stations where trains are receiving or discharging passengers.
d) approaching stations where train orders or clearances are to be picked up.
e) approaching meeting passing points or junctions.
f) approaching the end of two or more tracks where trains or engines are clear.
g) approaching trains on two or more tracks.
h) approaching trains in the opposite direction.
i) to assist in train identification by train and engine crews.

RULE 17A Exception: The full power of the headlight must be used approaching all public crossings at grade and until such crossings are reached regardless of their location.

RULE 18: Yard engines will display a headlight to the front and rear by night.