Retro-reflective tunnel markers

[Wolstan Dixie]

I need to measure a distance along the Central Line northbound tunnel. A frame grab from the 'Driver's Eye View' video is attached, which shows the tunnel as it approaches Liverpool Street. You will see down the left hand side a series of bright points spaced a regular distance apart. I don't think they are tunnel lights, there are too many of them, I believe they are retro-reflective tabs (like car number plates) reflecting back the drivers headlights. Using the video I plan to count these tabs between the two points I am interested in (the tunnel rings pass too fast for them to be feasible even slowed down). So I need to know the distance between them?

 

[Dstock7080]

They are tunnel light fittings.

 

[Wolstan Dixie]

They are tunnel light fittings.

Surely there are far too many of them - aren't the main tunnel lights on the right? They definitely dim as the train passes them, just as a retro-reflective panel would. They don't seem to be actually illuminating the tunnel, there are no pools of light on the track; would the tunnel lights normally be ON, surely not? I suppose they my be turned off tunnel lights painted with retro reflective paint. In any case - what is their spacing please?

 

[Dstock7080]

A view of Piccadilly Circus (Bakerloo)
tunnel lights on left
showing three lights and the car count-up markers 4-5:
(Bakerloo car 16091mm ÷3 =5,363mm) approx-apart

https://flic.kr/p/2qVaUNh

© Luke Agbaimoni

 

[bluegoblin7]

Surely there are far too many of them - aren't the main tunnel lights on the right? They definitely dim as the train passes them, just as a retro-reflective panel would. They don't seem to be actually illuminating the tunnel, there are no pools of light on the track; would the tunnel lights normally be ON, surely not? I suppose they my be turned off tunnel lights painted with retro reflective paint. In any case - what is their spacing please?

Tunnel lights are normally off.