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How long before bed should you stop looking at screens?

By Spektrum Glasses Editorial Team · Published 2026-08-12 · Updated 2026-09-11 · Facts re-checked 2026-09-11 How this page is written and checked: our editorial method · how we verify claims

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Short answer

No single cutoff is proven; the mechanism (retinal light signaling the brain’s clock) is continuous right up until a screen goes dark. General sleep-hygiene guidance often suggests dimming or stopping bright-screen use roughly one to two hours before bed, but device brightness, duration, and room lighting all matter more than the exact minute count.
  • Light around 460-480 nm is the wavelength band most tied to circadian/melatonin signaling in the eye.
  • No RCT has established one proven hour count; 1-2 hours before bed is common general guidance, not a tested figure.
  • A meta-analysis of 3 randomized trials (n=49, actigraphy-measured) found no significant change in sleep onset, duration, or efficiency from blue-blocking glasses.
  • Our yellow evening lens filters 98.3% at 460-480 nm and 98% across 400-500 nm (COLTS report O-SPG111015).
  • Lowering screen and room brightness matters at least as much as which lens is worn.

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How screen light reaches the body’s clock

The eye has a separate pathway for timekeeping, distinct from image-forming vision. Specialized retinal cells (intrinsically photosensitive retinal ganglion cells) feed light information directly to the suprachiasmatic nucleus, the brain region that runs the roughly 24-hour circadian clock. These cells are most sensitive to light in the blue-to-blue-green part of the spectrum, with peak sensitivity commonly placed in the 460-480 nm range. When enough light in that band reaches the eye late in the day, the clock can shift later and melatonin release can be delayed or suppressed. This is why the effect of screen light depends on timing, not just brightness. The same amount of light has more influence on the clock in the few hours before a person’s usual bedtime, when the circadian system is most sensitive to a phase delay, than it does at noon. A screen left on until the moment someone tries to fall asleep keeps that signal active for as long as it is in front of the eyes.

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Is there a proven number of hours

No. There is no controlled trial in the citations we rely on that pins down an exact number of hours before bed at which screen light stops mattering. What exists instead is general sleep-hygiene guidance, commonly in the range of about one to two hours before bed, recommending dimmer light and less bright-screen use as bedtime approaches. That range is a practical rule of thumb, not a measured threshold. Several variables move the real answer for any one person: screen brightness and distance from the eyes, how long the exposure lasts, whether other lights in the room are also on, and how sensitive that individual’s circadian system happens to be. A phone at low brightness held at arm’s length for five minutes is not the same exposure as a bright monitor at close range for two hours. Because of that variability, consistency in bedtime and evening light habits is easier to act on than chasing an exact cutoff time.

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What the research says about blue-light glasses and sleep

Because this is the best-studied part of the wider blue-light field, it is also where the honest caveats matter most. A meta-analysis of three randomized, crossover trials (49 participants total, sleep measured with actigraphy) looked at whether blue-light-filtering glasses changed sleep onset latency, total sleep time, sleep efficiency, and time spent awake after falling asleep. None of those four measures showed a statistically significant difference. The authors describe any benefit as small, and state that current trial evidence does not support a significant effect on these outcomes. A separate review in Therapeutic Advances in Ophthalmology reached a similar conclusion for blue-light-filtering spectacle lenses generally: minimal or no significant difference from standard lenses on contrast sensitivity, color discrimination, and task performance, with efficacy for eye strain and circadian or sleep-related outcomes still contested in the literature. Lenses may change how much light reaches the eye; they have not been shown in controlled trials to reliably change how well or how quickly someone sleeps.

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Where a filtering lens may help, and where it does not

Given that evidence, a lens’s contribution should be described in terms of what it measurably blocks, not in terms of a sleep outcome. Our clear lens (COLTS Laboratories report O-SPG111015, A2LA-accredited to ISO/IEC 17025) transmits 91.6% of visible light, meaning it reads as near-clear rather than tinted, while filtering 63.0% at 420 nm and 33.1% at 450 nm. That level of filtration is modest in the part of the spectrum most tied to circadian signaling, which is consistent with the lens being designed for general screen and daytime use rather than evening light management. A clear lens alone does not filter the full 460-480 nm band; for comparison, a competitor clear lens we tested filtered only about 52% averaged across the blue band despite blocking 100% of UV. Our yellow evening lens, measured in the same report, is a different design intent: it filters 98% of the 400-500 nm blue band, 99.9% of high-energy visible light, and 98.3% specifically at 460-480 nm, the band most associated with melatonin suppression, at around 65% visible light transmission. That heavier, visibly tinted filtration may help reduce the light signal reaching the eye during evening screen use. It has not been tested by us or in the cited trials as a treatment for a sleep condition, and it does not substitute for reducing screen brightness, screen time, or overall room light in the evening.

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Practical steps with more evidence behind them

Ahead of an exact hour count, the more actionable levers are the ones that change how much light reaches the eye in the first place: lowering screen brightness, using a device’s built-in night or warm-color display mode, reducing other light sources in the room, and increasing physical distance from the screen. Each of these reduces total light exposure directly, rather than relying on a lens to filter it after the fact. A consistent bedtime and a consistent pattern of dimming lights in the hour or so before it are also easier to sustain than trying to hit a precise cutoff every night, and they address the same underlying mechanism: giving the circadian system a clear, repeated signal that the day is ending. None of this requires a specific product, and none of the citations above show that any lens, on its own, reliably changes sleep timing or quality.

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Where these numbers come from

Every measured figure quoted here is transcribed from a third-party laboratory report, published in full with the wavelength band and the report number: lab results. Our rule for what may appear on this page at all is on how we choose what to publish.

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