Sorry, bit of a random question...

I was doing a Gatwick - Glasgow shuttle last night on one of the older 737s. During the safety briefing, they made the usual comment about "floor level lighting guiding us to the exits in the event of an emergency". Inspired by the recent discussion on here about missing life jackets, I actually made an effort to pay a bit more attention to my surroundings. It may have just been the fact I'd had a long week at work but I genuinely couldn't see anything that would have provided some sort of floor level lighting.

Out of sheer curiosity, where exactly is it / does it come from?

As far as i could see, the floor on the 737s is fully carpeted other than the runners in which each row of seats is fixed. In between these runners, there is blue plastic covering that doesn't look like it would illuminate. I couldn't see anything lighting related underneath or on the base of the seats around me either.

I could be completely wrong, but I'm sure when I fly on other plane types, the floor runners have a fluorescent type clear plastic cover that looks like it would guide me somewhere in the dark.

What am I missing? I'm sure the answer is extremely simple!