why is bright light bad for sleep?

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Bright light exposure, particularly in the late evening hours, can disrupt sleep quality and the ability to fall asleep. This is primarily due to the suppression of melatonin production, a hormone that induces sleepiness and assists with the sleep process. explains that viewing bright artificial light between the hours of 10 PM and 4 AM is not recommended since it can negatively affect circadian rhythms by mimicking sunlight, which can keep the brain alert and active when it should be preparing for sleep. Overhead artificial lights are especially problematic because they simulate sunlight due to the way the eyes' optics and neurons are structured. This can essentially trick our circadian clock, leading to difficulties falling and staying asleep 1.

Additionally, bright light exposure at night, not just blue light, suppresses the release of dopamine, a neuromodulator associated with mood and alertness. This can lead to an increase in depression-related symptoms and affect mental health adversely 2 3.

Optimize Your Sleep

Andrew explains the importance of avoiding bright artificial lights between 10:00 p.m. and 4:00 a.m. to improve sleep quality. He also recommends using low lights at night and bright artificial lights during the day to optimize sleep-wake cycles. Additionally, viewing evening sunset light can offset some of the negative effects of artificial light at night.
Huberman Lab
Sleep Toolkit: Tools for Optimizing Sleep & Sleep-Wake Timing | Huberman Lab Podcast #84
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Moreover, also mentions that exposure to light during typical sleep hours activates specific neural pathways that could reduce happiness and increase feelings of disappointment, as well as potentially lead to learning deficits and other negative effects 2.

Even children's sleep environments can be affected, as those who sleep with a nightlight or in dimly lit rooms have a higher likelihood of developing myopia (nearsightedness) compared to those sleeping in total darkness 4.

For these reasons, it is essential to have dim or no artificial light exposure during the night and to sleep in as dark an environment as possible.

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