What is the circadian dead zone?

The "circadian dead zone" refers to the middle of the day when exposure to bright light, including sunlight, does not effectively shift our circadian clock. During this period, the light—despite being bright and potentially having positive effects on mood and well-being—does not help in anchoring our sleep-wake cycle. This phenomenon is likened to pushing a swing at the bottom of its arc, where minimal or no effective change in momentum occurs. In other words, attempting to adjust your circadian rhythm by exposure to bright light during this midday period is biologically ineffective 1 2.