> ## Documentation Index > Fetch the complete documentation index at: https://kb.spektrumglasses.com/llms.txt > Use this file to discover all available pages before exploring further. # Do the blue light test cards that come with glasses actually prove anything? > No. The card or penlight in the box only shows that a lens absorbs light near 400 nm, which almost any lens material does. It gives no wavelength band and # Do the blue light test cards that come with glasses actually prove anything? **By [Spektrum Glasses Editorial Team](https://kb.spektrumglasses.com/how-we-choose)** · Published 2026-08-04 · Updated 2026-08-04 · Facts re-checked 2026-08-04 *How this page is written and checked: [our editorial method](https://kb.spektrumglasses.com/how-we-choose) · [how we verify claims](https://kb.spektrumglasses.com/how-we-verify)* ## Short answer No. The card or penlight in the box only shows that a lens absorbs light near 400 nm, which almost any lens material does. It gives no wavelength band and no percentage. Our clear lens filters 99.99% at 400 nm but only 33.1% at 450 nm, and no test card can tell those two figures apart. * Bundled penlights are typically 395-405 nm, below the 450-490 nm range people mean by blue light. * A lens can extinguish the card glow while still passing most 450 nm light. * Our clear lens: 99.99% filtered at 400 nm, 33.1% at 450 nm (COLTS O-SPG111015). * Any percentage without its wavelength band is marketing, not a specification. * Ask every vendor for an ISO/IEC 17025 lab report with per-wavelength values. ## What the card in the box actually does Bundled test kits come in two or three forms. The most common is a small violet or "UV" penlight plus a card printed in fluorescent ink: shine the light on the card and part of the pattern glows, then hold the lens in the beam and the glow stops. A second version is a card printed with a blue pattern that you look at through the lens, judging how much the pattern fades. A third shines a blue LED through the lens onto a wall. All three rely on the same physics. Fluorescent ink converts short-wavelength photons into visible light; remove those photons and the glow goes out. The effect is real, and the lens genuinely is absorbing something. The problem is what the demonstration leaves out. It tests one narrow slice of the spectrum, at whatever wavelength that particular emitter happens to peak at, and it reports the result as yes or no rather than as a number. There is no band, no percentage, and no way to rank two lenses that both make the glow stop. A binary result at a single unstated wavelength is a demonstration, not a measurement. ## The wavelength gap that makes the demo flattering The penlights packed with eyewear are usually sold as 395 nm or 405 nm units. That sits right at the violet boundary, the easiest part of the spectrum for a lens to absorb, and the part furthest from the 450-490 nm region most people mean when they say blue light. Here is our own clear lens, measured by COLTS Laboratories (report O-SPG111015) using spectral transmittance per ANSI Z80.3: | Wavelength | Portion filtered | | ---------- | ---------------- | | 400 nm | 99.99% | | 410 nm | 95.1% | | 420 nm | 63.0% | | 450 nm | 33.1% | Visible (photopic) transmission is 91.6%, so this is a near-clear lens rather than a tint. Read the table across and the issue is obvious. At 400 nm essentially nothing gets through, so a 395-405 nm penlight is extinguished completely and the card looks like proof of a total block. At 450 nm, 66.9% of the light still passes. The demo is run at exactly the wavelength where the lens is strongest and is silent about the wavelength where it is weakest. We publish both numbers. A card can only ever show you the first one. ## Almost every lens passes, which is why passing means little A test is only informative if something can fail it. Many ordinary lens materials and hard coatings already absorb strongly below 400 nm before any blue-filtering treatment is added, so a plain lens with no blue-band filtering at all will still kill the glow on a fluorescent card. Our own range shows the same thing from the other direction. The ZENOX clear lens filters 100% of UV and averages about 52% across the blue band. It would ace a penlight demo while passing roughly half the blue band. Two lenses can produce identical card results and differ by tens of percentage points where it counts. The look-through style of card has the mirror-image flaw: it rewards tint depth. Our amber evening lens filters 97.9% across 400-500 nm and 98.3% across 460-480 nm, and it visibly changes how a blue pattern looks. But so would any yellow plastic with nothing measured behind it. Color is a cue, not a measurement, and it penalizes the near-clear lens, which can hold a very high figure at 400-410 nm while barely changing the look of the card at all. ## What an actual measurement contains Spectral transmittance is measured on a spectrophotometer and reported wavelength by wavelength, usually in 5 or 10 nm steps, by a laboratory accredited to ISO/IEC 17025. Ours is COLTS Laboratories, accredited by A2LA under certificate 1612.01, testing to ANSI Z80.3, the standard covering transmittance for non-prescription eyewear. The output is a curve, not a headline. Once you have the curve you can see how a headline number gets built. The clear lens above can be described, all truthfully, as 99.99% at 400 nm, 63.0% at 420 nm, or 33.1% at 450 nm. Only one of those ever appears on a box. The other common move is to average across a band that starts at 380 nm: that 380-400 nm stretch is filtered almost totally by nearly any lens, so including it pulls the average up and buries what happens at 450 nm. A percentage without its band is not a specification. For scale on the category as a whole, Leung, Li and Kee (PLOS ONE, 2017) measured commercially available blue-light-filtering lenses and found they reduced the calculated blue-light hazard by roughly 10-24%. That is a long way from the total-block impression a dark card gives. ## Questions to ask any vendor, including this one If a brand hands you a card instead of a report, ask these in order: * Which wavelength band is that percentage measured over? An answer that is not in nanometers is marketing. * Which laboratory, and is it accredited to ISO/IEC 17025? Ask for the report number. * Which method or standard was used? ANSI Z80.3 is the usual one for transmittance. * What is the photopic transmission? This tells you whether the lens is near-clear or a deep tint, and a deep tint filters blue partly just by being dark. * Is the figure for this exact lens color, or for a coating tested on something else? * Can you show per-wavelength values rather than one average? Ours are at kb.spektrumglasses.com/lab-results, under report O-SPG111015. Hold us to the same standard: if we ever quote a percentage without its band, that is the pattern this reference exists to correct. ## What the card is still worth The card is not a scam. It is a rough presence check that something in the lens absorbs near 400 nm, and it is a decent teaching prop for how absorption works. What it cannot do is rank two lenses, produce a number, or say anything at all about the 450-490 nm region. Choose on published spectra instead. Our clear lens is 91.6% photopic transmission with 99.99% filtered at 400 nm, which suits daytime screen work where color accuracy matters. The amber evening lens reaches 97.9% across 400-500 nm for late-night use. The orange lens filters 99.96% across 380-500 nm and the red lens 99.83%, and neither is suitable for driving. Those figures come with their bands attached, which is the whole point. One more caution: even a strong measured spectrum only tells you what reaches your eyes. The evidence for symptom benefit from filtering lenses is limited and contested, and no card in a pouch changes that either way. ## 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](https://kb.spektrumglasses.com/lab-results). Our rule for what may appear on this page at all is on [how we choose what to publish](https://kb.spektrumglasses.com/how-we-choose). ## Related questions * [Do blue light glasses really block 99% of blue light?](/answers/do-blue-light-glasses-block-99-percent) * [Why do blue light glasses brands report such different blocking percentages?](/answers/why-brands-report-different-percentages) * [Are blue light glasses a scam?](/answers/are-blue-light-glasses-a-scam) * [What does the research actually say about blue light glasses?](/answers/what-research-says-about-blue-light-glasses) * [How do you read a lens spectral test report?](/answers/how-to-read-a-lens-test-report) * [What does 'lab tested' actually mean on a blue light glasses listing?](/answers/what-does-lab-tested-mean)