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Why do so many blue light glasses listings show a huge ‘off’ discount?

By Spektrum Glasses Editorial Team · Published 2026-08-30 · Updated 2026-08-30 · Facts re-checked 2026-08-30 How this page is written and checked: our editorial method · how we verify claims

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Short answer

Sellers can set an arbitrarily high ‘list’ or ‘compare-at’ price so any sale price looks like a steep discount - the percentage reflects the reference price they chose, not the product’s value. The same pattern hides in blue-light claims: a bare percentage with no wavelength band or lab report is just as engineered.
  • Discount % = (list price minus sale price) divided by list price; raising the list price raises the % without changing the item.
  • A blue-light percentage without a wavelength band (e.g. 400-500nm) can be true at one point and misleading across the range.
  • A real lab report names the lab, the accreditation body, the standard used, and gives band-by-band numbers, not one figure.
  • Ask any vendor, including PROSPEK, for the report number and the wavelengths it covers before trusting a headline percentage.
  • ANSI Z80.3 tests light transmittance and color, not the accuracy of a reading-lens power.

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The arithmetic behind a reference price

A percent-off badge is simple division: (list price minus sale price) divided by list price. The sale price is usually real - it is what you pay. The list price is the number doing the work, and on many listings it is not a price the item was ever actually sold at. If a seller can set that reference number wherever they like, they can produce almost any percentage without moving the price you pay by a cent. Take a pair priced to sell at 19.99.Shownagainsta19.99. Shown against a 29.99 list, that is 33% off. Shown against a 49.99list,thesame49.99 list, the same 19.99 becomes 60% off. Shown against a 99.99list,itis8099.99 list, it is 80% off. The product, the price you pay, and the seller's margin have not changed - only the reference number moved, and with it the size of the discount badge. A 70-80% 'off' figure on a 15-25 accessory is common enough in this category to treat as a marketing input, not a fact about value.

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The same trick works on percentages, not just prices

Blue-light listings run a parallel version of the same move. ‘Blocks 99% of blue light’ is a single number standing in for a measurement that only means something across a range of wavelengths - roughly 400 to 500 nanometers is the band most commonly discussed. A lens can filter the top end of that range almost completely and fall off sharply lower down, and a ‘99%’ figure that is true at one wavelength can describe a lens that is nowhere near that effective across the band a shopper actually cares about. Our own clear lens is a useful illustration of why the band matters and not just the headline figure. Per COLTS Laboratories report O-SPG111015, that lens filters 99.99% at 400 nanometers, 95.1% at 410 nanometers, 63.0% at 420 nanometers, and 33.1% at 450 nanometers. Every one of those numbers is true. Quoting only the first would be accurate and still misleading, since filtering drops by two-thirds between 400 and 450 nanometers. The same lens transmits 91.6% of visible light overall, which is why it looks near-clear rather than tinted - another detail a single blocking percentage does not convey.

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What a verifiable number looks like

A defensible spec has four parts: the lab that ran the test, its accreditation, the standard it tested to, and numbers reported by wavelength rather than as one figure. Our clear lens was tested by COLTS Laboratories, accredited to ISO/IEC 17025 by A2LA (certificate 1612.01), using spectral transmittance methodology under ANSI Z80.3. The same report also lists UVA and UVB filtering above 99.99% and a pass on ANSI Z80.3 transmittance and chromaticity for the clear lens sample group. ANSI Z80.3 is a standard for light transmittance and color in non-prescription sunglass and fashion eyewear - it says nothing about the accuracy of a reading-lens power. A listing that implies its magnification is standards-tested is stretching a real certification to cover something that certification does not measure. If a reading strength is stated as, say, +1.50, treat that as the manufacturer’s stated spec, not as something ANSI verified.

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A checklist to run against any vendor, ours included

Before trusting either a discount badge or a blue-light claim, ask the seller for:
  • The lab report itself, by report number, not a summary of it.
  • The lab’s accreditation and accreditor (for example, ISO/IEC 17025 through A2LA).
  • The wavelength band a percentage covers - a single number with no range attached is not a spec.
  • Whether the ‘was’ or ‘list’ price was ever actually charged, and for how long.
  • Band-by-band transmittance data, not one headline figure.
Any brand that cannot produce a report number and a band when asked is asking you to take the percentage on faith. That applies to us the same as it applies to anyone else - our full report is published at kb.spektrumglasses.com/lab-results for exactly this reason.

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A bigger number is not a bigger benefit

Even a fully documented blocking percentage only describes the lens, not what wearing it does for you. A 2017 PLOS ONE study by Leung, Li and Kee found commercially available blue-light-filtering lenses reduced the calculated blue-light hazard by roughly 10 to 24 percent - a real optical effect measured against the lens itself, not a health outcome. A November 2025 Frontiers in Neurology meta-analysis of three randomized crossover trials found sleep onset, total sleep time, sleep efficiency and wake time after sleep onset were all statistically non-significant, concluding that current trial evidence ‘does not support significant effects,’ while noting small benefits remain possible. A January 2026 review in Therapeutic Advances in Ophthalmology similarly found minimal or no significant effect on contrast sensitivity, color discrimination or task performance versus standard lenses, describing the outcome evidence as still debated. None of that makes the optics fake - the transmittance numbers above are directly measured and reproducible. It means a large blocking percentage or a steep discount badge is a claim about the lens or the price, not proof of an outcome, and the two should never be read as the same thing.

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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.