Every sunrise and sunset sends the body a signal, keeping the circadian clock running on a roughly 24-hour cycle. This clock evolved so organisms could adapt to Earth’s daily rotation, syncing their biology to the pattern of day and night. Artificial lighting has freed human societies from relying on the sun to go about daily life, extending activity well into the night, but this convenience comes with a trade-off.

It is not your living room lamp one needs to worry about, as standard indoor lighting, usually between 100 and 500 lux, stays safely within range. The real risk comes from extreme evening brightness from modern high-brightness screens and electronic displays, or occupational lighting in high-precision fields.