In the glow of nearly 300,000 lives mapped against the brightness of their neighborhoods at night, researchers have uncovered not an answer about how artificial light ages us, but a deeper question about whether we truly know how to measure aging at all. A large UK Biobank study found that the same nighttime light exposure produced opposite biological age signals depending on which algorithm was consulted — one suggesting accelerated aging, the other the reverse. The contradiction is less a failure of the science than a reminder that the body's unfolding is more complex than any single clock c