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Which reading strength (diopter) do you need?

By Spektrum Glasses Editorial Team · Published 2026-08-13 · 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

Reading strength is chosen by testing, not looked up from age: try ordinary print at a normal arm’s length and pick the lowest power that reads sharp without straining or leaning in. Diopters commonly run +0.50 to +3.00. A single-vision lens has one fixed focal distance, will not correct astigmatism, and does not replace an eye exam.
  • Diopters typically run +0.50 to +3.00; some styles also come with no added magnification.
  • A single-vision lens has one focal distance: it will not correct astigmatism or replace an eye exam.
  • Reading distance and screen distance differ; pick the strength for whichever distance you use more.
  • ANSI Z80.3 checks light transmittance and color, not the accuracy of a reading power.
  • Compare readers on lab-measured transmittance, coatings, and an accredited report, not diopter and price alone.

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Choosing a diopter strength

Reading strengths across the category commonly run from +0.50 to +3.00, with one style offering as many as nine steps within that range, and some frames also sold with no added magnification at all for people who want the frame and lens tint without extra power. There is no formula that maps age to strength reliably enough to shop by. The practical test: hold ordinary print, a book or a phone, at a normal arm’s length, roughly 14 to 16 inches, and find the lowest strength where the smallest text you actually read stays sharp without leaning in or holding the page at an odd angle. If a strength you already own works, that is the number to reorder rather than a fresh guess. Because a single-vision lens is ground to one fixed focal distance, picking a strength is trial and error by design, not a diagnosis. If near text needs correcting for astigmatism, or a strength that used to work stops working, that is a signal to get an eye exam and a prescription lens, not to reach for a stronger pair off the shelf.

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Reading distance and screen distance are different jobs

A book sits close, typically 14 to 16 inches away. A monitor sits farther, usually 20 to 28 inches. A single-vision reading lens is ground to bring one of those distances into sharp focus; used at the other distance, it is still a compromise, a smaller one or a larger one depending on the gap between the two. Marketing that treats a diopter as a universal near-task number glosses over this. The honest approach is to choose the strength that matches whichever distance takes up more of your day, and to expect the other distance to be slightly softer at the edges of your focus range. If time is split roughly evenly between book and screen, two single-vision pairs at two strengths is the accurate fix; a single lens marketed to do both perfectly is describing something a single focal distance cannot deliver.

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What actually separates one reading lens from another

The category is bought almost entirely on strength and price, which leaves out most of what actually differs between two lenses at the same diopter. Base material, anti-reflective coating on both lens faces, and measured light transmittance across specific wavelength bands all vary between products and none of that shows up in a diopter number. Two lenses at the same strength and the same price can differ in how much visible light reaches the eye, how much of the high-energy visible range near 400-450 nm they filter, and how much UV they block, and only one of those differences is visible to the eye. The way to check any of it, on any brand, is a spectral transmittance report from an accredited lab, not a bare percentage on a package.

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Reading a transmittance report, band by band

A few checks work on any lens, ours included. First, does every filtering percentage state the wavelength band it was measured over. A number like a blocking percentage with no band attached cannot be verified and should be treated as unsupported. Second, is overall visible-light transmission (VLT) disclosed separately, since a heavily tinted lens can post a high blue-light-filtered percentage while cutting overall clarity. Third, is UV filtering reported apart from visible-light filtering. Fourth, did an accredited lab run the test, for example one certified to ISO/IEC 17025, and does the report identify how many samples were tested. Our own clear lens, tested by COLTS Laboratories under report O-SPG111015 (A2LA-accredited to ISO/IEC 17025, certificate 1612.01), filters 99.99% of light at 400 nm, 95.1% at 410 nm, 63.0% at 420 nm, and 33.1% at 450 nm. The taper is real: filtering is highest at the shortest wavelengths and falls off through the violet-to-blue range, and stating that plainly is part of the check, not a footnote to hide. Visible-light transmission is 91.6%, which is why the lens reads as near-clear rather than tinted. Both UVA and UVB are filtered above 99.99%. The same report also carries a pass on ANSI Z80.3 transmittance and chromaticity testing, all samples in the clear-lens group, filter category 0, cosmetic lens. That standard governs how a lens transmits light and holds color; it says nothing about how accurately a reading power is ground, so a Z80.3 pass is a claim about light and color, not about magnification. Full figures are published at kb.spektrumglasses.com/lab-results.

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How this stacks up against ready-made magnifiers

Ready-made magnifiers, as a product class, are typically specified by diopter and price and little else; that is often the entire spec sheet. A coated optical lens carries measurable coatings, tint, and wavelength-band transmittance data because it is manufactured and tested as an optical component rather than molded as a magnifying blank. The useful comparison is to run the same checks from the previous section, band-stated percentages, disclosed VLT, separate UV figures, an accredited lab report, against any reading eyewear you are considering, ours included, and against a ready-made magnifier. In practice a magnifier usually has no such report to check at all, which is the actual difference worth shopping on, not the diopter number by itself.

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What a reading lens does not do

A single-vision reading lens has one fixed focal distance. It does not correct for astigmatism, and it is not a substitute for an eye exam. If you have never had a proper eye exam, or your near vision has changed noticeably, that exam is the right next step before buying any reading strength off the shelf, ours or anyone else’s. No reading lens changes what strength is medically appropriate for a given prescription; it magnifies for near tasks, at one distance, and nothing more. Treat the diopter number as a starting point for the arm’s-length test above, not as a settled specification, and treat the lab-measured figures in this article as the part of the spec sheet that a diopter number alone will never tell you.

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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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