Is your sleep tracker lying to you? The truth about melatonin.

What I was trying to say in the talk is this: the circadian system of humans can probably be affected by relatively dim light, but to get an effect you have to expose it for six or seven hours. And you have to be aware that the effect you're measuring — suppression of melatonin and shifting of the melatonin rhythm — is two log units more sensitive than regulating sleep-wake timing.

So extrapolating from changes in melatonin to sleep-wake behavior is also inappropriate.