Nothing. I don't think I've ever seen an illuminated underpass other than one that's now condemned below a train station, that one had regular 4ft fluorescent fittings protected by custom built grates, only 2-3 worked and the rest was dark.
Everyone avoids them at night so they don't need lights, and if I have to go through one I carry a pocket torch, the bus route I take is pitch dark at night, because all of the wiring for streetlights was overhead and stolen by copper thieves, there's only a few privately owned glarebomb LED floodlights but they only light up garage entrances.
Public streetlights aren't too common in my country, because of arcane legal shenanigans, the section of pavement (if any) between the road and your house is technically a part of your property, so the lighting is up to you. Only state-managed buildings have proper lighting outside, trainstations, and some large parks, but that's really it.
Some neighbourhoods have agreed to use the same type of lights so they purchase in bulk and they all look the same, -awful 6500K LEDs- but other parts of the city are whatever people had: floodlights, cheap flush mount luminaires, hanging holders with, there's strings too, and some old dead linear halogens that are dark patches now.
