The quality of your sleep, the time you fall asleep, and your state upon waking are primarily determined by exposure to sunlight before 10 a.m. over the preceding 2 to 3 days.

noli's read

This advice is based on the functioning of our internal biological clock, or circadian rhythm, controlled by the suprachiasmatic nucleus. Research confirms that morning light exposure (ideally natural) is the most powerful signal (zeitgeber) for synchronizing melatonin production and establishing the sleep-wake cycle (meta-analysis, Sleep Medicine Reviews). While the impact on circadian regulation is scientifically robust, asserting that it is the 'primary' factor (the 'biggie') simplifies a multifactorial reality. Other variables such as body temperature, physical activity, diet, and evening blue light exposure also play crucial roles documented by numerous studies (RCT). The term 'non-negotiable' is a stylistic emphasis here that highlights the biological importance of the light signal without invalidating the influence of other lifestyle habits. In short, it is a major regulatory lever, although sleep architecture depends on a set of complementary signals.

the sources

1. 1Blume C, Garbazza C, Spitschan M 2019
2. 2Brown TM et al. 2022