100 lux
One lit night strains the body
In a randomized PNAS study, a single night of sleeping in ordinary room light raised nighttime heart rate and measurably worsened next-morning insulin resistance (Mason, Zee et al., 2022).
The science of dark sleep
Independent sleep and circadian research keeps landing on the same conclusion: light during sleep — even a little — changes how your body rests and repairs. Here is what the studies actually measured.

The science of dark sleep
100 lux
In a randomized PNAS study, a single night of sleeping in ordinary room light raised nighttime heart rate and measurably worsened next-morning insulin resistance (Mason, Zee et al., 2022).
5 lux
Dimmer than a streetlamp bleeding around a curtain edge — yet polysomnography showed more arousals and shallower sleep (Cho et al., 2016).
Deep sleep
Lights-on nights produced less slow-wave (deep) sleep and reduced delta and spindle power on EEG (Cho, Joo et al., 2013).
88,905
Higher night-time light exposure was linked to higher all-cause and cardiometabolic mortality in a large wearable-sensor cohort (Windred, Cain et al., 2024).
Made to measure
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