I don't believe for one second that I'm the first to report this, but spotted it while finishing off my Bakerloo journies, and couldn't find anything obvious referring to it in the forum. I also guess it shouldn't be a surprise that the global lighting has an effect inside the tunnels when people have already spotted things like rain or snow also have an unusual amount of impact on adhesion as well. Disclaimer - I play with all graphic settings at their lowest, so I accept that things might look less dramatic when all the graphical sparklies are enabled, but if I try turning them on to check, my laptop fans start doing their Concorde impression and the game turns into Train Slideshow World... For consistency, all three screengrabs were taken with the 245-09 E&C-H&W 12:08, at Spring Clear, with the only change being the "Cloud Level" settings. Low Cloud: Medium Cloud: Highest Cloud: To remove any element of doubt about whether this is some ambient light level, or due to the main "sun" light, here is a shot from inside the tunnel heading towards Harrow (taken from the 12:08 E&C-H&W with Spring Clear) and the reverse shot heading back towards E&C (taken from the 12:09 Queens-E&C with Spring Clear) Driving the tunnels with full cloud is a lot more fun! I believe other people have already reported that the speed limit signs don't "glow" with the reflection from the cab headlights, so there's no point in me mentioning it again here!
And final reference shot, here is one from 222D-23 E&C-Queens Park at 22:36, also at Spring Clear, but when it's night outside
