Many of the mechanisms for light impacting biological functions show a clear dose-response relationship - fewer photons hitting the retina leads to less effect.
As a rough estimate, one decade (10x) of the eye’s light adaptation, at most, comes from aperture variation - the pupil expanding and contracting. The rest comes from intensity-driven modification of the sensing and image processing systems in the eye - rods that are completely saturated with signal above a few dozen lux become the primary sensors in very low light.
In other words - just because the moon provides enough light to see and even read doesn’t mean that it will cause insomnia.
As a rough estimate, one decade (10x) of the eye’s light adaptation, at most, comes from aperture variation - the pupil expanding and contracting. The rest comes from intensity-driven modification of the sensing and image processing systems in the eye - rods that are completely saturated with signal above a few dozen lux become the primary sensors in very low light.
In other words - just because the moon provides enough light to see and even read doesn’t mean that it will cause insomnia.