Flickering lights on Tube?

[aurora83]

Why do the lights sometimes flicker in the carriages on the tube? I know it happens on the the district line and probably elsewhere.

And on the same note, why do aircraft have to turn off the cabin lights when flying over London at night?

[woodchopper]

I would have a guess the power is picked up on the rails and generally make a good contact in most places - the flickering would be caused by the pick up not making good contact,
as for the cabin lights - so the terrorists can't see them to shoot them down.

[Trotbot]

Cabin lights are dimmed on all approaches at night in case there is a crash as emergency lighting is not bright and you won't normally have time to wait for your eyes to adjust to the light

[RATTER15]

Woodchopper, I cant see that trains would rely on picking up power for the lights on trains from the line, surely they would have batteries that run the lights, the batteries however would likely be charged from the rails. I think that flickering lights are probably down to poor connections.

[woodchopper]

Found this link - appears the lights do run off the mains- must have a pick up somewhere -

http://www.findarticles.com/p/articles/mi_qn41 53/is_20060626/ai_n16502543

[RATTER15]

OK woodchopper, I'm a defeated man, I am wrong lol, but you would think that commonsense would say to run the lights on batteries chargeable from the lines and have more backup batteries for emergencies. That way the lights wouldn't flicker and if the power on the lines failed, it would not effect the lights on the train.

[redmug100]

Most of the lighting in a tube car gets its power from the rails apart from a couple of emergancy lights that run off a battery. The lights flicker when the train runs over a gap in the current rails. The District line runs over National rail lines between Turnham Green and Richmond and South of Putney Bridge and the gaps here are longer than normal. It also has very complex flat junctions around Earls Court and Aldgate East.

[Lonnie]

Speaking from experience, as a tube Train Driver of some years, redmug has given you the correct answer, if a train halts so that the shoes that pick up the traction current are over a railgap, all the main lights in that unit, (usually two care to a unit), go out, except for the emergency lights, which are run off Batteries, what you have to worry about, is if those batteries are good or not, because if they run out of power, then you will be left in complete darkness.

Thats the basics of your question from the train side.

[aurora83]

Thanks for the answers, i thought it was probably that