Skip to main content

​
Why do blue light glasses brands report such different blocking percentages?

By Spektrum Glasses Editorial Team · Published 2026-08-04 · Updated 2026-08-04 · Facts re-checked 2026-08-04 How this page is written and checked: our editorial method · how we verify claims

​
Short answer

Because a blocking percentage is meaningless without the band it was measured over. The same lens can be reported as 99.99% or 33.1% depending on whether a brand quotes a single wavelength, an average across 400-500 nm, or a weighted hazard figure. Different measurement choices, not different lenses, explain most of the spread.
  • A percentage without a wavelength band is not a claim, it is a headline.
  • Our clear lens filters 99.99% at 400 nm but 33.1% at 450 nm.
  • Filtering falls sharply as wavelength rises, so brands quote the short end.
  • Weighted hazard math gives much smaller numbers than peak transmittance.
  • Ask for an ISO/IEC 17025 lab report with a full transmittance curve.

​
One lens, two honest-sounding numbers

Start with our own clear lens, measured by COLTS Laboratories (report O-SPG111015, spectral transmittance per ANSI Z80.3). These are the published points: Every one of those numbers is true. A marketing team that wants a big number quotes 400 nm and writes “blocks 99.99% of blue light.” A team that wants to be conservative quotes 450 nm and writes 33.1%. Same lens, same report, a 67-point spread. The reason is physics: filtering in a near-clear lens drops steeply as wavelength rises. Blocking 400 nm is easy because 400 nm is at the edge of what the eye sees, so removing it costs almost no visible light. Blocking 450 nm is hard because 450 nm is plainly visible blue, and removing it turns the lens yellow or amber. So when two brands report wildly different percentages, they are usually not selling different lenses. They are quoting different points on a curve that every blue-filtering lens has.

​
At least four definitions of the blue band are in circulation

There is no single industry-mandated definition of “blue light” for consumer claims. In practice you will see percentages quoted over:
  • 380-500 nm, the widest reading, which includes near-UV and pulls averages up
  • 400-500 nm, the common definition of visible blue
  • roughly 415-455 nm, often labeled HEV or high-energy visible
  • 460-480 nm, the narrow region most discussed in circadian research
  • a single wavelength, usually 400 nm or 410 nm
Our own numbers move with the definition, which is the point. Our amber evening lens measures 97.9% across 400-500 nm, 99.9% of HEV, and 98.3% at 460-480 nm. Our orange lens measures 99.96% across 380-500 nm, and our red lens 99.83% over the same range. If we picked whichever band flattered each lens most and dropped the band label, we could publish a tidy row of near-identical numbers that would tell you nothing. When a page says “blocks 99%” and never names a band, the most likely explanation is that the band would make the number smaller. That is not proof of dishonesty, but it is a reason to ask before you buy.

​
Raw transmittance and weighted hazard are different math

A third source of divergence is which quantity is being averaged. Raw spectral transmittance asks how much light at each wavelength gets through. A weighted metric multiplies that curve by a hazard or sensitivity function that assigns more importance to some wavelengths than others, then integrates. The two produce very different headline figures from identical measurements. Leung, Li and Kee (PLOS ONE, 2017) measured commercially available blue-light-filtering spectacle lenses and found they reduced the calculated blue-light hazard by roughly 10-24%. Readers sometimes treat that as evidence that 99% claims are fabricated. It is better read as evidence that the two numbers answer different questions. A weighted hazard reduction of 15% and a 99% figure at 400 nm can describe the same lens. This is also why you should be suspicious of any comparison table that lines up percentages from different sources. Unless every entry uses the same band and the same method, the ranking is arithmetic noise. Comparing a competitor’s single-wavelength peak against your own band average is a way of winning a comparison without measuring anything.

​
A clear lens cannot filter the whole band, and tint is the trade

Our clear lens has a photopic (visible) transmission of 91.6%. It looks essentially clear, which is why people wear it at a desk all day. That same property is what caps its filtering in the middle of the blue band: light you can still see is light the lens did not remove. The measured 33.1% at 450 nm is the honest consequence. Our ZENOX clear lens averages about 52% across the blue band, with 100% UV. That is a reasonable number for a clear lens, and it is nowhere near 99%. Any brand claiming a genuinely clear lens that removes 99% of 400-500 nm is describing something that would not be clear. If the lens in the product photo has no visible color cast, the band-average figure has to be modest. Heavier filtering requires visible tint. Our amber evening lens reaches 97.9% across 400-500 nm and looks amber. Our orange and red lenses reach higher still and look strongly colored. Neither the orange nor the red lens is suitable for driving, because the color shift interferes with recognizing signals and road markings. Higher percentage is not automatically better; it buys filtering by spending color accuracy.

​
What to demand from any vendor, including this one

Five questions separate a measured claim from a written one:
  1. What wavelength band does the percentage cover, stated in nanometers?
  2. Is it a peak value at one wavelength, or an average across the band?
  3. Is it raw transmittance or a weighted hazard calculation?
  4. Who measured it, and is that lab accredited to ISO/IEC 17025?
  5. Can I see the transmittance curve, not just the summary number?
Accreditation matters because it is the difference between an independent measurement and an in-house estimate. Our clear and amber lens data comes from COLTS Laboratories, A2LA-accredited to ISO/IEC 17025 under certificate 1612.01, measured per ANSI Z80.3. Our orange and red figures were measured in 2026 by our lens manufacturer’s optical laboratory, which is an in-house measurement, and we label it that way rather than blurring the two. Our full report is published at kb.spektrumglasses.com/lab-results. If a vendor cannot answer question 1, you do not have enough information to compare anything. If they cannot answer question 4, you are being asked to trust a number that no third party has checked.

​
Differences that persist even when everyone is honest

Not all variation is marketing. Coating thickness, substrate material, and lens curvature vary between batches and between styles, so two lenses from the same production line can differ by a few points at a given wavelength. Measurement geometry matters too: readings taken at the optical center of a flat sample and readings taken through a curved finished lens are not identical. Rounding compounds it. A lens measured at 96.4% across 400-500 nm becomes “over 96%” in careful copy and “99%” in careless copy, and nobody in the chain feels they lied. The practical takeaway is that a difference of a few points between two lab-reported, band-labeled figures is not worth agonizing over. A difference between 33% and 99% for lenses that look equally clear almost always means one of them is not quoting a band average. That is the gap worth catching.

​
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.