Measuring Cognitive Load Under Circadian Lighting in a Tropical Sky Lobby
Four months of data from 240 users of a tropical office tower reveal a counter-intuitive pattern: lower mid-day illuminance can lift task-completion. We document method, instruments, and limits.
Over four months we logged 240 occupants of a tropical sky lobby against a circadian lighting schedule, then cross-referenced self-reported alertness with anonymised task-completion data from the building's own systems.
Lower mid-day illuminance lifted task-completion. We did not expect the curve to bend that way.
The headline finding is counter-intuitive: a modest reduction in mid-day illuminance correlated with higher afternoon task-completion, not lower. Our working hypothesis is glare relief — the lobby's west glazing was overwhelming the fixtures at noon.
We publish the method and the instrument list in full because the effect is small and we want it stress-tested. Circadian design in the tropics cannot be lifted wholesale from temperate guidance.