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Tail lights
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Y Ddraig Coch
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Just a guess.... but possibly because they only have the one lamp on the rear of freight trains it could be to ensure anything coming up towards it doesn't think it is a red signal up ahead. if you see two lights on a passenger train its obvious, not so with just the one on a freight train.
Just my two pence worth. Happy to be corrected with facts!
Just my two pence worth. Happy to be corrected with facts!
Bletchleyite
Veteran Member
I think it's simply flashing to save battery life.
edwin_m
Veteran Member
The traditional tail lamp was an oil lamp so did not flash, though it did flicker a bit. There were some battery-powered ones back in the 70s with steady lights, but with traditional filament lamps I suspect the battery would be nearly flat after one journey.
The reason for the portable ones flashing is therefore largely due to battery life. Locos and units don't have this concern (at least not to the same extent) so have steady tail lamps, although you could argue that flashing ones would be more conspicuous.
I don't think confusion with a red signal is a big issue since both of them mean STOP! Although two built-in tail lamps are provided and normally lit on locos and units I believe they can continue their journeys if one of them fails (though with modern LED clusters this is pretty unlikely).
The reason for the portable ones flashing is therefore largely due to battery life. Locos and units don't have this concern (at least not to the same extent) so have steady tail lamps, although you could argue that flashing ones would be more conspicuous.
I don't think confusion with a red signal is a big issue since both of them mean STOP! Although two built-in tail lamps are provided and normally lit on locos and units I believe they can continue their journeys if one of them fails (though with modern LED clusters this is pretty unlikely).
philthetube
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on the underground we were supposed to replace a failed tail light with the stabling light or a bardic.
DarloRich
Veteran Member
The red lamp is supposed to allow the signal man to confirm the train is complete and has come apart somewhere. I guess it flashes to make it easier to see.
Passenger train do carry a flashing tail lamp when there is not fixed alternative such as a DVT, built in tail lights,or an attached and powered up locomotive.
dk1
Veteran Member
Brought the ex-works half of the 156 involved in the Sudbury line collision a few years ago back from Dereham to Crown Point dragged by a 153. None of us thought to take a tail light so my little hand lamp had to do the honours with a bodged up way of attatching it. Was surprised it survived th whole way.
A flashing light also allows you to have a brighter light from an LED than you can have from a steady light. You can put a higher current through the LED for a short time than you can safely do for a continuous current. This gives a brighter light but conserves battery power.
SpacePhoenix
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Would a unit/loco have to be failed if only one tail light was working (would it be allowed to run in service with a portable flashing one either in the cab window or externally attached)?
dk1
Veteran Member
With just one it would continue in service but be attended to asap. In these days of LED it tends to be both as it's usually a power fault. In that case red light in the window or portable tail lamp & jobs a gooden.
E_Reeves
Established Member
Does anybody know how long a flashing tail light would usually last?
Until the battery goes flat. Not a facile answer, just it depends on the initial state of charge, the condition of the battery and environmental conditions.
I'm not in the industry so this is a SWAG* - I would guess a minimum of 12 hours (since there would need to be a driver change after that).
*SWAG - Scientific wild-assed guess.
E_Reeves
Established Member
I've seen tampers parked up for over 24 hours with the flashing tail lights on though.
Oh, I know that. I was just thinking out loud what the absolute minimum life would be.
SpacePhoenix
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Do any portable lights that use LEDs use li-on batteries?
Are you assuming they are rechargeable ? How long would a normal battery last ? My old lamp used a 4.5V square battery.
Has anyone checked Unipart to see the specs on a portable lamp ?
Yes, I was thinking that modern ones would be rechargeable. I'm pretty sure I've looked through a window at a station and seen some on charge.
signallerscot
Member
Dorman mk3 LED flashing tail lamps use 2x 6V 50Ahr air alkaline batteries which are not rechargeable. Battery life is approximately 10000 hours of continuous use. Info easily found on google!
http://www.unipartdorman.co.uk/assets/mk3_portable_tail_lamp.pdf
http://www.unipartdorman.co.uk/assets/mk3_portable_tail_lamp.pdf
Whilst there might be some rechargeable tail lamps, somewhere, all the ones that I have seen use a pair of throwaway 6 volt lantern batteries, the ones with springs on top.
These have the merits of simplicity and being fairly cheap if purchased in bulk, they are much less used domestically than in years gone by and therefore seldom pilfered.
Rechargeable batteries would not be suited in my view.
Battery life is weeks or months, it varies a great deal according to the quality of the batteries used.
A good quality zinc carbon 6 volt lantern battery should contain 4 cells each "F" size and should have a capacity of at least 10AH. Inferior batteries contain 4 D cells plus a spacer and therefore have a lower capacity.
Alkaline batteries may have a greater capacity, but not always, and may not be worth the considerably higher price.
Air/alkaline batteries exist and have much greater capacities but find little favour due to the higher price, and the limited life once the seal is broken.
EDIT TO ADD was not aware of the preceding post whilst I was typing. The new tail lamp featured DOES make use of air/alkaline batteries of great capacity and hence a long life of well over a year continually.
A cynic like me would suspect that when the expensive air/alkaline batteries are dead that they will be replaced with cheapo zinc carbon ones as used at present.
These have the merits of simplicity and being fairly cheap if purchased in bulk, they are much less used domestically than in years gone by and therefore seldom pilfered.
Rechargeable batteries would not be suited in my view.
Battery life is weeks or months, it varies a great deal according to the quality of the batteries used.
A good quality zinc carbon 6 volt lantern battery should contain 4 cells each "F" size and should have a capacity of at least 10AH. Inferior batteries contain 4 D cells plus a spacer and therefore have a lower capacity.
Alkaline batteries may have a greater capacity, but not always, and may not be worth the considerably higher price.
Air/alkaline batteries exist and have much greater capacities but find little favour due to the higher price, and the limited life once the seal is broken.
EDIT TO ADD was not aware of the preceding post whilst I was typing. The new tail lamp featured DOES make use of air/alkaline batteries of great capacity and hence a long life of well over a year continually.
A cynic like me would suspect that when the expensive air/alkaline batteries are dead that they will be replaced with cheapo zinc carbon ones as used at present.
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Thinking about it some more, I think it may well have been hand lamps I saw charging rather than tail lamps.
My hand lamp (new version
) uses 3x AA Duracel. Its LED and has about as much use a proverbial in a proverbial. The Bardic could be used for a replacement lamp when required. The new POS is basically a hand torch with triple colours. Yay for technology :/ The new dispatch bat is rechargeable and runs out pretty quick by all accounts.
Some of the personal equipment has moved towards rechargable. Are standard batteries more reliable ? With portable lamps you would need a central charging point so the practicality may also be limited.
signallerscot
Member
You won't see so many of these about but the Dorman portable headlamp is rechargeable with a 12V lead acid battery but uses an 8W halogen lamp rather than LEDs.
http://www.unipartdorman.co.uk/assets/portable_headlight.pdf
http://www.unipartdorman.co.uk/assets/portable_headlight.pdf
That all depends on charging discipline. NiMH batteries don't have a noticeable memory effect so if you are in the habit of charging regularly - e.g. end of shift, lamp goes on charge - then they should be more dependable than regular batteries (unless, of course, the regular batteries are replaced on schedule rather than on demand).
E_Reeves
Established Member
It says they last over 10,000 hours with two 50Ahr Air Alkaline batteries
Just saw this post...
Just saw this post...
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Yes, and existing designs of tail lamp would also have a much longer battery life if fitted with 50AH air/alkaline batteries rather than with 7AH or at best 10AH zinc carbon batteries.
However the average railway purchasing manager will balk at the price of the air/alkaline batteries as compared to the cheapo zinc carbon ones, especially if the expensive ones end up on someone else's train !
We still use them in my neck of the woods, though have to send them off to the depot for charging. Not entirely sure why the headlamps are rechargeable but the similar tail lamps aren't though!
The headlamp uses 8 watts, to supply that from disposable batteries would need a lot of batteries and replaced frequently.
4 of the common 996 lantern batteries would in total supply 8 watts, but only for about 24 hours with zinc carbon batteries.
The higher capacity air/alkaline batteries would not be suitable for a headlight because they only work at very low currents.
It is possible that an LED battery headlight will be developed, with a lower wattage than the halogen version, in that case operation from throwaway batteries would be more viable. A steady white light would still use a lot more power than a flashing red light with a consequent reduction in battery life.
The battery tail lights have little use outside of the railway industry and are therefore seldom stolen.
The battery headlights are rather desirable and somewhat vulnerable to theft. Restricting access to the battery chargers is a bit of a deterrent.
4 of the common 996 lantern batteries would in total supply 8 watts, but only for about 24 hours with zinc carbon batteries.
The higher capacity air/alkaline batteries would not be suitable for a headlight because they only work at very low currents.
It is possible that an LED battery headlight will be developed, with a lower wattage than the halogen version, in that case operation from throwaway batteries would be more viable. A steady white light would still use a lot more power than a flashing red light with a consequent reduction in battery life.
The battery tail lights have little use outside of the railway industry and are therefore seldom stolen.
The battery headlights are rather desirable and somewhat vulnerable to theft. Restricting access to the battery chargers is a bit of a deterrent.
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