Lux looks like red glowing crystals that are scavenged from beneath the sand in the desert in my story. It’s used as a light source (because there’s no sun), can power electronics and fuel transportation, and is melted down to coat weaponry, so it makes for very good trading.
And no one knows what exactly lux is and where it comes from ¯_(ツ)_/¯
Money in my stories is more referred to in the background instead of actually explained. It’s kind of like real world currency (coins and cards, not sure about notes yet). I haven’t fully developed it as it’s yet to ‘properly’ come up in the pain plot. But the general idea is this: