Circadian rhythms

Light Hygiene Science & Tips for Better Sleep, Fat Loss, Memory and More

by Mike Mutzel


Circadian lighting is the latest buzzword in health and medicine. Here’s a full breakdown of all things related to light exposure, sleep and circadian rhythms.




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More About this Episode:

Light Prescription and recommendations from the Expert Consensus Panel:

-Daytime light exposure: aim for 250 lux at the level of the eye for at least 20 minutes during the day

-Evening light exposure: starting at least 3 hours before bedtime, the maximum amount of light you should be exposed to is 10 lux

-Nighttime light exposure: just before and during sleep, the maximum light you should be exposed to is 1 lux at the level of your eye. (Hint: your iPhone is emitting light)



Brown, T. M. et al. Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults. Plos Biol 20, e3001571 (2022).

Tam, S., Brown, L. A., Wilson, T. S., the, S. T. P. O., (2021). Dim light in the evening causes coordinated realignment of circadian rhythms, sleep, and short-term memory. National Acad Sciences

Xu, Y., Yu, Y., Huang, Y., Wan, Y., Su, P., Tao, F., & Pollution, Y. S. E. (2022). Exposure to bedroom light pollution and cardiometabolic risk: A cohort study from Chinese young adults. Nutrition, Metabolism and Cardiovascular Diseases, 294.


Time Stamps:

00:00 Specialized cells within your retina sense light and influence your body’s circadian clock system, neuro-endocrine functions, mood, affect, memory, focus, sleep, attention, and hormone regulation.

00:35 Sleep is as important as a nutrient.

01:30 Artificial light at night can impair your attention the next day and impact melatonin and growth hormone release.

02:08 A Lux is a measurement of the intensity of light.

07:00 Mental health disorders should prompt an examination of light hygiene.

07:30 Light influences circadian rhythm, sleep, alertness, mood, and neuro, endocrine and cognitive function.


07:40 Retinal responses to light are important determiners of health, wellbeing and performance.

09:20 Receiving 100 lux or more light exposure in the evening, melatonin is significantly suppressed.

10:30 In intense light, retinal cells seem to transmit messages that it is daytime, relaying chemical cues to the main circadian clock hub suprachiasmatic nucleus (SCN) in your hypothalamus, which is part of your hormonal regulatory system.

11:50 Daylight recommendation is 250 lux at the level of the eye. Being in the car or wearing sunglasses does not count.

13:15 Minimize exposure in the 3 hours prior to your sleep time to just 10 lux measured at the eye. A candle releases about 1 lux. Your phone is about 50 lux.

14:25 Sleep environment maximum ambient light exposure is 1 lux.

15:40 Just 5 lux during sleep has been shown to have significant increases in a myriad of cardiovascular biomarkers.

16:10 Light affects the rate at which you age at a cellular level.

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