What is the Window Of Circadian Low time frame?

• A. 1200-1359
• B. 0200-0559
• C. 0500-1200
• D. 1700-2100

Answer: (B)

The window of circadian low is the daily period when alertness is at its lowest due to the body's natural rhythm. This dip typically occurs in the early morning, roughly from 0200 to 0559 local time, when the body’s core temperature is at its lowest and melatonin is higher. Because performance tends to decline during this window, it’s a key factor in planning rest and flight schedules to avoid operating during peak fatigue. The given early-morning span matches this circadian nadir, whereas times around noon, late morning into afternoon, or evening do not reflect the deepest part of the sleep-wake cycle. Keep in mind that individual factors like sleep debt or jet lag can shift the timing, but 0200–0559 is the standard reference for WOCL.