How the evening screen cut-off time is worked out
This calculator subtracts the lead time you chose from your bedtime to give a cut-off time, then multiplies your evening days per week by your average daily use to total the week. When the lead time is longer than the clock time of your bedtime, the cut-off falls on the previous day and the page labels it that way. The monthly figure is a plain multiplication on a four-week basis.
On blue-light filtering lenses, a Cochrane review (2023) pooled 17 randomized controlled trials with 619 participants across six countries, searched to March 2022. The review concluded that blue-light filtering lenses probably make no difference to eye strain, visual performance or sleep quality, and its authors put the short-term point plainly: such lenses may not reduce eye strain from computer work. No evidence on preventing retinal damage was found, because the included trials did not assess that outcome at all.
So this page promises no benefit from the lenses, and it names no figure for how long before bed screens should go off, because that number is not confirmed in an authoritative source; you enter your own lead time instead. Current as of October 2026, and not a medical diagnosis. Eye pain, a sudden change in your vision, or new flashes or floaters should be seen by an eye doctor.
Frequently Asked Questions
The Cochrane review (2023) concluded that they probably make no difference to eye strain, visual performance or sleep quality. Adverse effects were temporary and mostly mild, and were attributed to wearing glasses in general rather than to the filtering lenses.
The review found no evidence on preventing retinal damage. That is not a finding of no effect: the 17 included trials simply did not assess that outcome.
This page does not recommend one, because that figure is not confirmed in an authoritative source. Enter a lead time you can actually keep, see the cut-off time it gives, and watch how your weekly total moves.