The researchers tracked circadian phase, light exposure and activity levels in 25 nursing and medical staff in a Melbourne hospital intensive care unit, reports The New Daily.

As expected, the timing of when the test subjects were exposed to light and when they were in the dark or dim light had the greatest impact on when their body clocks shifted from alertness to tuning out and drifting toward rest.

The net result was that, for the first time, the mathematical model – built over a long period of time by a succession of researchers – could be generalised to estimate the timing of the body clock in shift-working staff.