Question 1

How long does it take to reset a circadian rhythm?

Accepted Answer

Research from CU Boulder (Wright et al., 2017) shows that a single weekend of natural light exposure can shift melatonin onset by 1.4 hours, or 69% of the benefit of a full week. Most people can achieve a meaningful reset in 2 to 7 days using structured morning light exposure and consistent sleep timing.

Question 2

What is a chronotype?

Accepted Answer

A chronotype is your biological tendency toward a particular sleep wake timing. Early birds (larks) naturally wake early, night owls naturally sleep and wake late, and most people fall somewhere in between (intermediates). Chronotype is largely genetic but is strongly influenced by light exposure.

Question 3

What is social jetlag?

Accepted Answer

Social jetlag is the mismatch between your biological clock and your social schedule (work, school). It is measured as the difference in sleep midpoint between weekdays and weekends. Roenneberg et al. (2012) found that each hour of social jetlag increases obesity risk by 33%.

Question 4

What time should I get morning light exposure?

Accepted Answer

The most effective window for advancing your circadian clock is within 30 to 60 minutes of your target wake time, ideally outdoors in natural sunlight. Bright light (1,000 lux or more) in this window suppresses residual melatonin and anchors your circadian clock to an earlier phase.

Question 5

How does light exposure reset the circadian clock?

Accepted Answer

Light activates intrinsically photosensitive retinal ganglion cells (ipRGCs) that send signals directly to the suprachiasmatic nucleus (SCN), the brain's master clock. Morning light advances the clock (makes you sleepier earlier) and evening light delays it (makes you sleepier later). Outdoor light is 13 times more effective than typical indoor lighting at driving this effect.