Lights in the London Underground tunnel - South Circle Line oddness

This happened about three weeks ago, 11:45pm on a Tuesday night. I was coming back from a late shift on the District Line and I'd just got on at Embankment heading towards Sloane Square. The train wasn't particularly full, maybe a dozen people in my carriage.

As we were coming into South Kensington, before the train fully emerged from the tunnel between Westminster and South Kensington, I noticed this weird phosphorescent glow on the tunnel wall - sort of greenish-white. Not the normal lights, not a torch, something different. It was there for maybe thirty seconds and then just... gone.

I asked the person next to me if they'd seen it and they looked at me like I'd grown a second head. None of the other passengers seemed to notice anything. I've used the Underground for fifteen years and never seen anything like it. Has anyone else experienced weird lighting phenomena in the Tube? Or is there any logical explanation for what I saw?

The London Underground has loads of old infrastructure and abandoned tunnels. What you probably saw was bioluminescence from fungi or moulds - they're definitely present in the Tube system and they can glow faintly under certain conditions. Phosphorescent paint is also used in various places for safety markings. Not paranormal, just industrial fungus basically.

South Kensington's on the Circle and District lines primarily, not the South Circle (that's not a thing, did you mean the Piccadilly?). Either way, there's massive electrical infrastructure all through the Tube tunnels. What you saw was probably reflected light from the third rail or electrification equipment. Still weird to see but not mysterious.

Actually this is interesting. There are occasional reports of weird light phenomena on the Tube, particularly around South Kensington and the Knightsbridge area. Some people reckon it's related to old Victorian-era infrastructure or even experimental lighting systems that were tested but never removed. Worth documenting if you see it again - time, exact location, duration, colour, anything else you noticed.

I've used the Underground for fifteen years and never seen anything like it

Could also be a maintenance light, a torch from a workman in the tunnel, or someone's light-up phone case reflecting oddly. The Underground does maintenance work constantly and you don't always see the workers. Less exciting explanation but more likely.