Does a blue-light filter on my phone really affect my sleep?
A blue-light filter on your phone probably has little effect on your sleep. If you really want to improve your sleep through light, switch your home lighting to warm yellow in the evening instead of cool white.
A blue-light filter app on your phone probably does not help. An observational study found no link between using such an app and better sleep. And an experiment involving Facebook use on a tablet showed that filtering blue light alone produced no sleep improvement: only the combination of removing blue light and eliminating distracting social content had a visible effect.
Blue-light filter glasses paint a somewhat mixed picture. Six smaller RCTs split neatly into thirds: three found an improvement, three found nothing. The certainty of that evidence is rated 'very low' by a Cochrane analysis. Two separate experiments with employees did find improvements in sleep and even in work performance, but those groups were small and the context specific. Evening types appeared to benefit more than morning types.
One thing stands out: the choice of your home lighting seems to have more influence than any filter on your screen. Cool-white LED or fluorescent light suppresses the production of the sleep hormone melatonin considerably more strongly than warm-white light. If you set your LED lamp to a warm colour temperature in the evening (around 2100K), that suppression drops to virtually zero. That is more effective than most blue-light filter lenses, of which only two with a brown tint performed genuinely well in the same laboratory study. Standard lenses do very little.
One further caveat: the Cochrane review found no evidence that blue-light filter glasses reduce eye strain. Side effects were rare, but were present in a proportion of users: think mild mood changes or headaches.
Based on a Cochrane review (6 RCTs, 148 participants), two small experimental employee studies (n=63 and n=67), an observational smartphone study, a tablet experiment, a meta-analysis of intraocular lens implants (8 studies, 1007 patients) and a laboratory study of 52 lamps. All human studies are small; the evidence for the app specifically is observational.
How bad is screen light in the evening for my sleep?
Screen light in the evening disrupts your sleep hormone and keeps you less sleepy at the wrong moment. Dim your screens after dinner, or wear amber-tinted glasses if you still need to work.
What does alcohol do to the quality of my sleep, and is there anything that can be done about it?
Alcohol helps you fall asleep faster, but measurably disrupts the rest of your night, even with just two drinks. If you want to sleep better, drinking less or no alcohol before bed is the most effective step.
Are sleep trackers accurate enough to help you improve your sleep?
A good wearable shows patterns over time. It overestimates your sleep duration as a rule, and it does not measure your sleep stages reliably. That is enough for following trends; with serious sleep problems, see a doctor.
Does the sleep tracking feature on my smartwatch have any value?
Your smartwatch gives a useful indication of your sleep pattern, but accuracy varies considerably by device and it is not a substitute for a proper sleep diagnosis. Use it as a personal trend monitor and discuss persistent complaints with your GP.
Does a consistent morning routine with daylight help you fall asleep more easily in the evening?
A consistent morning routine with daylight helps sharpen your biological clock, allowing you to fall asleep earlier and more easily in the evening. The evidence is not perfect, but consistent enough to make it worthwhile: step outside briefly shortly after waking up.
Does creatine affect your sleep?
Creatine may improve how your sleep feels, but objective measurements show no effect. Do not use it primarily as a sleep aid; if you are already taking it for sport, you need not expect worse sleep.