This is a sparkling and illuminating study, one of those rare books that could genuinely improve your life... Her experiment is extreme, but it is relatively easy to stay off screens just before bedtime. Newer devices now offer “night” modes, which cut the most stimulating blue element in the light output. We could and should dim evening lights more generally, too. They make us produce the sleep-promoting hormone melatonin later than we would do naturally, which means it is still in our systems when we wake up. That groggy feeling in your head in the morning? That’s a “melatonin hangover”.