Front Headlights

[phoenixcronin]

Why is it that all the Class 172 and 378's I see running around always run with the right "big" headlight and the left "small" headlight on. I find it looks a bit weird.

[rincew1nd]

AIUI, the right-hand headlight and left-hand marker light in "day" mode, at night it is reversed. Possibly because a daytime headlight is so you can see the train, whereas a night one is so the driver can see the road and signs?

[domh245]

More or less rincew1nd.

Any there are 2 types of lights on a modern train, marker lights and headlights. The marker lights are mainly to show the direction the train is travelling in, and these are the smaller lights, typically LED lights. The headlights proper (with proper bulbs) serve to draw attention to the train for track workers. The offside lamp is used during the day, and then the nearside during darkness, as it is angled slightly to the left and down, to illuminate trackside signs, but it is still mainly for making the train visible. When in a depot, both marker lights will be lit, and the main headlight not lit, to prevent dazzle.

On some trains, both marker lights will be lit in addition to the headlight, but on others, including the -star family of trains made by Bombardier, only 1 marker and 1 headlight are lit.

[rincew1nd]

Rather than marker lights showing the direction of travel (surely that's what tail lights are for?), is the marker light not there to aid distance perception? Certainly at night it's easier to tell how far away a car is than a motorbike.

[phil]

Nov 7, 2015 21:31:36 GMT rincew1nd said:

Rather than marker lights showing the direction of travel (surely that's what tail lights are for?), is the marker light not there to aid distance perception? Certainly at night it's easier to tell how far away a car is than a motorbike.

Marker (and indeed tail lights) are a hang back from the days of steam where Oil lamps were used, those at the front being switched on to give train information to signalmen in mechanical signalboxes. Over time the need for thios has disappeared and marker lights took on a new meaning - to tell staff which end of the train it was being driven from.

As far as visibility to track staff goes - you are not allowed to work closer than 6ft 6* from the nearest running rail during periods of darkness (or during fog / falling snow when viability is reduced such that sufficient sighting distance is not available to the lookout). As such judging the speed of an approaching train is not necessary because you will be in a place if safety to begin with. During the day when lookouts are in use then judging the speed of an approaching train is done primary by the yellow front end getting visibly larger as the train gets closer, plus the distance between the marker lights getting bigger. The headlight in itself does not contribute to this process other than to say "I'm here"

(* If the linespeed is less than 40mph the distance drops to 4ft and if the speed of trains is NO MORE than 20mph working with lookouts is permitted)

[undergroundwomble]

Whilst on the subject of headlights, and on London Overground trains I recently saw a main line train in the Docklands area which had a light built in to the "bumper" part of the front of the train. It was approximately on a level with the coupling. I have not seen a light that low down before and wonder what it was there for?

[domh245]

That is a feature of more modern Bombardier stock (classes 379, 377/6, 377/7, 387) and it is to light up the track ahead of the train so that the forward facing CCTV can record useful pictures. There is also a light in the pantograph well of these trains (where fitted with a pantograph) which illuminates the OHLE, again so that it can be recorded. An effect best seen at night:

387108 passes West Hampstead Thameslink by Matt Payn, on Flickr

[norbitonflyer]

Not sure where you would have seen any of those classes from a London Overground train in the Docklands area - maybe a 377 or 387 south of New Cross or a 379 on the Anglia lines, but neither of those are really Docklands.

[undergroundwomble]

Thanks for that explanation, it does make sense when you see the night-time pictures of the train fitted with this extra light.

norbitonflyer, To be honest I cannot remember exactly where it was I saw this train, it would have been somewhere in the Excel exhibition site or the Stratford (Olympic Park area)so possibly not really Docklands.