How strong is the evidence for Dark Sleep Environment?

Research on night-time light exposure is supported by a large prospective cohort study linking light exposure at night to higher cardiovascular disease incidence, alongside a microlongitudinal study finding night-to-night associations between light exposure and sleep health, and broader reviews on artificial light at night and circadian disruption. That evidence is currently rated moderate (48/100), built on 6 published studies -- a reasonable base, but not yet enough for full certainty.